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Posted: Wednesday, February 11, 2015 12:00:00 AM
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Phrenology is the study of the shape of the human skull in order to draw conclusions about particular character traits and mental faculties. Phrenologists believe that traits like intelligence are mirrored through elevations in the skull overlying particular areas of the brain. German physiologist Franz Joseph Gall developed the theory around 1800, but modern neurology and physical anthropology regard phrenology as a form of quackery. What is the difference between phrenology and craniometry? More...
Posted: Wednesday, February 11, 2015 3:35:48 AM

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Daemon wrote:

Phrenology is the study of the shape of the human skull in order to draw conclusions about particular character traits and mental faculties. Phrenologists believe that traits like intelligence are mirrored through elevations in the skull overlying particular areas of the brain. German physiologist Franz Joseph Gall developed the theory around 1800, but modern neurology and physical anthropology regard phrenology as a form of quackery. What is the difference between phrenology and craniometry? More...

Not sure we've made huge strides with consciousness since. Whistle

All good ideas arrive by chance- Max Ernst
Posted: Wednesday, February 11, 2015 6:21:10 AM

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Pure unadulterated silliness.
JUSTIN Excellence
Posted: Wednesday, February 11, 2015 7:31:37 AM

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Location: Veinau, Baden-Wuerttemberg Region, Germany
Physitians in their Anatomic Lectures, though the whole body lye before them, yet they read chiefely upon some more noble and Architectonical parts, the braine, the heart, the stomach, or the like.
—William Spurstowe,
EnglandsPatterne and Duty in Its Monthly Fast (1643)

With the collapse of the western Roman empire during the fifth century CE, original versions of Greek and Roman natural philosophy, including the anatomical works of Galen (c. 130-201 CE), are dispersed eastward. For the next 1,000 years,approximately, the classical Western learned medical tradition exists in fragmentary form in Greek, Latin, Arabic, and other near-eastern languages. During this period and later, humoral theories of bodily operation reign within two schemes of human organ hierarchy: Galen's, which posits a triumvirate of heart, brain, and liver, and Aristotle's, which emphasizes the heart. Alchemical schemes, which begin to appear during the Renaissance, usually emphasize the viscera, especially the stomach and spleen.

In 1810, Franz Gall published the first of four volumes on the structure and function of the nervous system. Much of his work was later shown to be correct. He identified the function of the gray and white matter and made a systematic analysis of the different parts of the brain. His work was sophisticated and insightful and should stand as a milestone in the study of neuroanatomy. Unfortunately, Gall went off on a tangent and tried to develop a discipline of neural analysis based upon the shape and location of bumps on the skull, “phrenology.” It is sad that it is for this diversion that Gall is generally remembered.

Developing a Personality

What makes behave people as they do? Are people ordinarily aware of what they are doing, or are their behaviors result of hidden, unconscious motives? Are some people naturally good and others basically evil? Or do all people have potential to be either good or evil? Is human conduct largely a product of nature, or is it shaped mostly by environmental influences? Can people freely choose to mold their personality, or their lives determined by forces beyond their control? Are people best described by their similarities, or is uniqueness the dominant characteristic of humans? What causes some people to develop disordered personalities whereas others seem to grow toward psychological health?

These questions has been asked and debated by philosophers, scholars and religious thinkers for several thousand years; but most of these discussions were based on personal opinions that were colored by political, economic, religious and social considerations. Then, near the end of 19th century, some progress were made in humanity's ability to organize, explain and predict its own actions. The emergence of neuroscience as the scientific study of human behavior marked the beginning of a more systematic approach to the study of human personality.

The 1990s has been designated as the Decade of the Brain, but some suggest that the twenty-first century will be the century of the brain, when the last great frontier in biology—an understanding of the most complex biological system, the human brain—will be breached. Already the considerable advances made in neuroscience over the past 50-100 years are being called upon to explain many things about human behavior. Interdisciplinary programs are appearing in our colleges and universities asking what various disciplines and fields can learn from neuroscience and vice versa.

In this post, we describe the maturation of the brain and how experience molds it, primarily by pruning. Dendritic and axonal fields of neurons are refined, synapses rearranged, and neurons even lost. There are critical periods for much of this plasticity, sensitive times early in life when various aspects of brain structure and function are particularly susceptible to alterations. We will discuss some new facets of brain development.


Language is certainly one of the critical features that most distinguishes humans from animals. There are those who believe that the ability to speak, read, and write—and thus to communicate ideas and images that can evoke within us sensations and feelings—is what initiated our rich inner mental lives that we talk of as awareness or consciousness.

When did language first develop in humans? Human skulls of 150,000 years ago are similar in size to our own, suggesting that these early ancestors had brains like ours and were capable of language.However, there is no evidence for human behaviors that we believe link to language—rituals and complex social interactions,conceptualization and planning, art and symbolic representation—until 40,000 years ago. Thus, there is a gap of about 100,000 years during which we know virtually nothing of what was going on. Some evidence of modern human behaviors prior to 40,000 years ago has been uncovered—burials, trade, and tool making—but most paleontologists believe that it was not until 40,000 years ago that humans were fully modern and that language was universal.

All humans possess language, and as Steven Pinker remarked in his book, The Language Instinct, whereas “there are Stone Age societies, . . . there is no such thing as a Stone Age language.” All human languages are sophisticated and complex. There are some primitive people who do not use writing, but all use complex language.(Indeed, writing is a rather new invention among all peoples. The earliest written records date back only about 6,000years.) It is also true that the ability to speak is not essential for language; sign languages used by deaf communities can be as sophisticated as spoken languages.

Serious attempts have been made to teach language to certain nonhuman primates, especially chimpanzees. Chimps in the wild can make about 36 different sounds, almost as many as English speakers. Each chimp sound typically conveys something different,whereas each sound we make (called a phoneme) usually means nothing. We string phonemes together to make words, and an educated English-speaking adult has a vocabulary of about 80,000 words.

Is it a difference in vocal tracts and speech abilities that prevents chimps and other nonhuman primates from forming words as we do? One way to test this is to teach chimpanzees sign language and this has been done, particularly by Duane Rumbaugh and Sue Savage-Rumbaugh at the Yerkes Regional Primate Center in Atlanta. They were able to teach young chimpanzees a vocabulary of about 150 words, but then the animals went no further.These chimps can communicate at about the level of a two-and-a-half-year-old child. However, this is the point at which a child’s language abilities are beginning to explode. By age 3, a child typically has a vocabulary of 1,000 words and by age 4 it might be 4,000 words. Thus, humans are quite distinct from all other animals in their language capability.

Language Areas

Language is controlled mainly by areas in the cerebral cortex, and two areas have been identified as being especially important: Broca’s area and Wernicke’s area. However, language also depends on our ability to discriminate speech sounds, as well as to make complex speech sounds. Thus, both auditory and motor systems contribute to speech and language, and other neural systems are certainly involved too.

One of the two cortical areas especially important in language, Broca’s area, is concerned mainly with the articulation and the production of speech. It is localized in the frontal lobes of the cortex near the region critical for the initiation of movements—the so-called primary motor cortex. Broca’s area is named for Pierre Paul Broca a nineteenth century French neurologist and anthropologist, who studied people who had lost the ability to speak, a condition known as aphasia. He discovered that many of his patients had damage in that part of the cortex that now bears his name. These patients knew what they wanted to say, but their ability to articulate words was impaired. They often could not form proper speechsounds. The first patient Broca studied was called Tan because all he could utter was “Tan, tan, tan” (with an occasional speechsound thrown in).

Lesions in Broca’s area also lead to writing deficits and even deficits in sign language, so it is clearly involved in more aspects of language than speech articulation. For example, there is general agreement that Broca’s area plays an important role in grammatical processing. The second language area is called Wernicke’s area, named after Carl Wernicke, a German psychiatrist. It is found in the temporal lobe of the cortex, between the so-called primary auditory and visual areas, where sounds and visual stimuli are first processed in the cortex. Patients with lesions in this area typically have difficulty with speech comprehension and with reading and writing. They can articulate words perfectlywell, but their word choice is inappropriate. The words they utter are clear, but their sentences usually make no sense.

As we noted earlier, many neural systems are involved in language, so lesions in other parts of the brain can also cause language deficits. However, Broca’s and Wernicke’s areas are clearly key for producing meaningful language. Curiously, Broca’s and Wernicke’s areas are found on just one side of the brain, usually in the left cortical hemisphere (95 percent of the time), whereas most other cortical areas have representation in both cortical hemispheres.

Thus, if there is damage to the left hemisphere, a patient might be totally aphasic even though the right hemisphere is completely intact. Substantial damage to the right hemisphere does not usually compromise language ability. On the other hand, if the left hemisphere is damaged early in life, many children are able to use the intact right hemisphere to learn language.

Learning Language

Linguists estimate that there are 6,000 languages spoken around the world today and thousands more were spoken at one time and are now lost. How can the human brain accommodate so many languages with so much variation? Noam Chomsky, the Massachusetts Institute of Technology linguist, studied various languages and noted that there are striking similarities among all of them. He proposed that all languages, present and past, have common grammatical principles. For example, all languages use subjects,verbs, and direct objects. The order in which these elements are positioned in sentences differs among languages, but all languages have these three classes of words. Thus, he suggested that the developing brain possesses innate neural circuits that allow for the acquisition of any of the thousands of languages now or previously spoken.

Certainly all languages share many characteristics, as Chomsky suggested, but whether the brain has innate circuitry to deal with all languages as he proposes or whether it develops at least partially as a result of experience is not certain and is a matter of much debate. It is almost certain that both innate mechanisms—nature—and learned experiences—nurture—are involved in language acquisition, although the extent to which, and how,each contributes is not settled. Clearly, innate neural circuitry must place constraints on the ability to make and perceive language,but learning is critical too, as we shall see.

Some of the most compelling evidence that there are innate mechanisms underlying aspects of language—in support of Chomsky’s basic idea—is the phenomenon of creolization that occurred in seventeenth-century America. Slave owners brought together people from different African tribes that spoke quite different languages. The slaves quickly created a simplified pidgin language, based usually on the plantation owner’s language. Pidginhad a crude word order but lacked a clear grammar. The children of the slaves heard only pidgin, but did not adopt it. Rather,they typically created their own languages—Creole languages—that had a grammatical structure similar to that of all other human languages.

Another bit of evidence comes from the discovery of a gene defect in a large multigeneration family that has an inherited speech and language disorder. The affected family members have problems with articulating speech sounds, identifying speechsounds, understanding sentences, and with grammatical and other language skills. The gene is inherited dominantly so that about half of the offspring of affected family members have inherited the defect—14 out of 27 offspring so far studied. The gene, called FOXP-2, probably codes for a transcription factor, a protein that interacts directly with DNA, turning genes on or off. In support of this idea, the protein contains a specific region that is known to bind a target region of DNA. Exactly what the gene does is not yet known, but an obvious suggestion is that it has a role in the development of brain circuitry related to language and speech. The gene appears to have arisen about 200,000 years ago, approximately the time that human brains assumed their modern size and when, it is thought, humans were first capable of language.

Children appear to learn language in much the same way allover the world. By one year of age, children begin to speak a few recognizable words. By 18 months, they begin to combine words and by three years, they can engage in conversation and are speaking in the language or languages to which they have been exposed. Learning a language requires no formal instruction, although hearing it spoken is critical. Indeed, it is thought that even hearing language in utero is involved, in that at birth infants prefer the language spoken by their mothers as distinct from other languages.And clearly, exposure to language early in life accelerates language acquisition and is essential for language development.On the motor side of language acquisition, babies begin to babble before 18 months and this also is critical for the development of language. We have all heard babies babbling “dadada” or “bababa,” and this is the beginning of speech production by infants.

Clearly, young children acquire language much more readily than do adults, and thus it is generally agreed that there are early critical or sensitive periods for language acquisition from about 12 months to six years. Children who are exposed to a language in the first six years quickly learn to speak that language perfectly without any detectable accent. After six years it is more difficult to learn a new language, and by puberty the ability to learn a new language is dramatically reduced.

Learning a new language at 40 is similar to learning one at 20, although some people are much more adept at learning new languages than others. Linguists say that the accent for a language learned as an adult is never perfect, and that a language expert can always tell if someone has learned a language as an adult. Even many children who learn a new language between the age of 6 and puberty retain accents characteristic of their native language. The example often cited is Henry Kissinger, former Secretary of State,who came to the United States when he was eight years old. Hehas a distinct accent. His brother came at age 6 and is reported to have no accent.

Why do we lose the ability to speak a new language perfectly as we grow up? Youngsters are sensitive to a broad range of sounds,but they lose the ability to distinguish or make certain sounds unless they hear or produce them during the first six years or even earlier. For example, adult Japanese people cannot distinguish an “r” from an “l” sound, yet seven-month-old Japanese children can distinguish these sounds as readily as American children. By 10 months of age, native Japanese infants have already lost some of their ability to discriminate “r” from “l” sounds. American babies,on the other hand, are better at discriminating these sounds at 10 months than they were three months earlier.

The conclusion from these studies is that the period from six to twelve months is already critical for babies to learn to discriminate all different language sounds. In all languages 869 sounds or phonemes have been identified and infants six to eight months old can discriminate all of them. After that they use just a subset—those that they hear and thus distinguish. Conversely, young children can imitate virtually any sound an adult makes, but this ability is also lost with age. By one-and-a-half years, babies start to make sounds characteristic of the languages to which they are exposed, and their ability to make sounds characteristic of other languages slowly disappears.

What happens if a child is not exposed to any language for the first six to 10 years? Fortunately, there are few recorded cases, but the results are remarkably similar. The most recent example, in the 1960s, is of a young girl, Genie, who at the age of 20 months was tied up and locked in a darkened room by her psychotic father. The father and her intimidated brother only growled or barked at her for more than 10 years. When she was 13 1/2, she was discovered and found to be quite mute. Intensive attempts were undertaken to teach her language, but after three years of training, she was still unable to speak well; she had the language competence of a four-year-old at most. The speech she produced was labored and inarticulate. She often was unable to grasp the meaning of speech without contextual clues or gestures, and she was clearly retarded in terms of normal linguistic and comprehensive abilities. Confounding her situation was the fact that she was almost completely isolated during her imprisonment—from both sensory and emotional events—and there was some question as to whether she was mentally retarded.

However, Genie’s failure to learn language was similar to that of Victor, the “Wild Child of Averyron” who lived alone in the woods in the early part of the nineteenth century. It is conjectured he was abandoned as a young child but managed to survive until he was captured at the age of 12 or 13. Victor, like Genie, never developed normal language skills, despite heroic efforts to teach them to him. There are also cases in the literature of people deaf from very early days having their hearing restored as adults who do not learn to speak effectively.

What is going on in the brain’s language areas during the critical period? We cannot, of course, record from neurons in these areas as we can for the visual areas of animals during the critical periods and so we can only conjecture. It is tempting to suggest, however, that, as in the visual cortex during its critical periods, neurons can gain or lose territory, synapses rearrange and new ones form, depending on language experience. This notion might be extended to suggest that by the age of six months to a year,neural circuits have formed to discriminate and make all possible language sounds and to acquire grammar. If the circuitry is not used, it is rearranged to accommodate the native language(s) or perhaps even lost. The adage “Use it or lose it” might fit for language development as it did for visual development.

Just as with the visual system, different attributes of language acquisition appear to have their own critical periods. The critical period for making sound discriminations might be the earliest; up to six or seven months infants can discriminate all possible human speech sounds, but by 10 to 12 months, this ability is already compromised somewhat and infants might begin to show deficits. With regard to sound production, it appears that up to about five or six years, children can learn to speak a language perfectly, without an accent, although, again, some investigators believe that this critical period extends to puberty, at least for some children.

The point to emphasize is that critical periods in language acquisition don’t slam shut at a specific age, but there is a gradual decline in various language acquisition abilities over time, superimposed on a considerable variability among people.With regard to grammar acquisition, a careful study of Korean and Chinese children who came to the United Kingdom showed that after 10 years of experience with English as a second language, those who arrived before age seven had a mastery of English grammar equivalent to that of native English speakers, whereas those who arrived later had grammatical skills that related to their time of arrival in the UK. Of the latter group, those who arrived earlier were more proficient than later arrivals. The grammatical skills of people who arrived after age 17 were never equivalent to those of earlier arrivals and it made little difference at what age they arrived. Thus, for grammar the critical period can extend to puberty, but it begins to close as early as seven years of age, at least for some children.

With regard to learning vocabulary, there appears to be no critical period. We can learn new words, names, and expressions throughout our lives. Certainly, children learn new words faster than adults, and for many people, vocabulary learning levels off in high school, but college students show a considerable increase in vocabulary learning as do graduate and professional school students as they are introduced to the vocabularies of new fields and areas of study.


Because language is unique to humans, its development is difficult—indeed impossible—to study neurobiologically as can be done with the visual system by studying visually inexperienced or visually deprived animals. However,some systems in animals have certain similarities to human language and these systems can be analyzed in detail. Birdsong is one such example. . .

Of the 8,500 species of living birds, about half are songbirds. Birdsong is used for a number of purposes, including attracting mates, defending territories, or simply indicating a bird’s location or presence. Birds of the same species have similar songs, but the songs can vary quite significantly over relatively short distances. For example, sound spectrograms of white crowned sparrows recorded in two locations around San Francisco Bay, Berkeley, and Sunset Beach. The spectrograms for birds in each of these areas are similar, but surprisingly varied in the two areas. Thus, as with human speech dialects, birdsong from different geographical areas varies.

Birdsong, like human language, has great diversity. Some species, like white-crowned sparrows, have one basic song that shows geographic diversity, but other species sing many different songs. Certain wrens, for example, might have as many as 150 songs. The number of song units (syllables) varies considerably with birdsong, from 30 for the canary to roughly 2,000 for a brown thrasher. Again, this is comparable to the variety of speech sounds(phonemes) found in different human languages—which range from as few as 15 to more than 140. Another characteristic of song birds is that some, zebra finches, for example, sing exactly the same song throughout their lives, whereas others, canaries, for example, vary their songs; they incorporate new syllables into their songs from year to year.

How does birdsong develop? Again, we see striking similarities with human language acquisition. Young birds typically learn the songs they hear from their parents. They show a strong preference for songs of their own species, but if exposed only to songs of another species, they can acquire those songs. Indeed, young birds can develop more elaborate songs than their own species sing—if they are exposed to such songs appropriately. That young birds have a strong preference for their own species’ songs suggests that they have an innate neural circuitry for those songs; however, like humans, they appear capable of acquiring certain other songs as well, so they must also have a circuitry template appropriate to accomplish this.

When first learning to sing, birds often exhibit a subsong, noises that might be comparable to babbling in human babies. The young birds next typically produce sounds that contain recognizable bits of the adult song, and finally, they begin to sing the adult song. Song learning involves two components, song memorization and song vocalization, and a critical or sensitive period clearly exists for song memorization and perhaps for song vocalization as well. The song memorization period begins when the birds are about two weeks old and lasts for about eight weeks in white crowned sparrows and in another model species, the zebra finch.

Although birds can hear before they are two weeks old, they do not memorize their species’ song if it is presented to them before the second week. Conversely, if they do not hear any song until they are three to four months old, they never sing a normal song. Interestingly, birds raised in acoustic isolation throughout the critical period do eventually sing, but only an “isolate” song that lacks both the spectral and temporal qualities of the normal song. On the other hand, if a young bird is exposed to the normal song for only a few days during the critical period, it immediately acquires the song and sings it accurately as an adult. Young birds can learn the songs of other species, as noted above, but if the alien song differs substantially from their normal song, the birds develop isolate song singing. Furthermore, whereas birds can learn alien songs if exposed only to them, they take much longer to do this than to learn their own species’ song.

If, during the beginning of the critical period for song memorization, a baby zebra finch is exposed to its normal song for one week — or long enough for the bird to memorize the song — subsequent isolation from the normal song or exposure to alien songs makes little difference. The critical period for song learning is terminated in essence after the bird has been exposed to the normal song for a week. On the other hand, if the bird is kept in acoustic isolation for several weeks after the opening of the critical period and then hears the normal song, it learns it rapidly, but this capacity clearly declines with age and is lost by three to four months. How the song is presented can also be important. Whereas presenting the normal song with loudspeakers works fine with young song sparrows, it does not with song sparrows older than 50 days old. The older birds need a live tutor bird from which to learn the song. In other species, however, a live tutor is not necessary to train an older bird—a recorded tutor works fine.

Learning to sing by birds — that is, song vocalization — is a distinct process from song memorization, and song vocalization in white-crowned sparrows occurs several months after song memorization. Song vocalization might also be constrained by a critical period, although this isn’t entirely certain. Learning to vocalize clearly requires auditory feedback, so if a bird is deafened by destroying its inner ear after song memorization but before it begins to sing, it does not develop a normal song. If a bird is deafened after it has learned to sing, it usually continues to sing a normal song; acoustic feedback is no longer needed.

Most birdsongs are sung only by males, and song vocalization is affected by the male hormone, testosterone. Exposing a juvenile bird to high levels of testosterone causes it to develop its song prematurely, but in an abnormal way. On the other hand, birds that are castrated before they learn to sing never develop normal singing patterns. It appears, therefore, that hormonal levels affect song vocalization in birds, and perhaps hormonal levels regulate the critical period for vocal learning. The period for vocal learning may close as the birds reach sexual maturity, at the time that testosterone and other steroid hormone levels rise in the animals.

Neural Control of Birdsong

Specific areas have been identified in the forebrain of birds that control song production and the learning of song vocalization.(The bird forebrain is analogous to the mammalian cortex.) There might also be areas specialized for song memorization, but these haven’t yet been identified. The song production and vocal learning areas were first identified because of the increased size of certain nuclei (groups of neurons) in male brains. Two distinc tsystems have been identified — one in the posterior forebrain that is responsible for song production and the other in the anterior forebrain that is key for vocal learning.

Two posterior forebrain nuclei are involved in song production, the higher vocal center (HVC) and the robust nucleus of the arcopallium (RA). When a songbird begins to sing, a wave of neural activity spreads from the HVC to the RA and then to a nucleus in the hindbrain (the hypoglossal nucleus) that contains the motor neurons controlling the vocal muscles. Lesions of the HVA or the RA make birds incapable of producing songs.

The anterior forebrain pathway also consists of two nuclei, area X and the lateral portion of the magnocellular nucleus of the anterior nidopallium (LMAN) as well as the dorsolateral thalamic nucleus called the DLM. If a lesion is made in the LMAN while a bird is learning to sing, the bird goes no further in song development but is frozen at the level already reached and is incapable of developing a mature song. Lesions in area X also prevent birds from acquiring a stable adult song. Circuitry studies indicate that HVC innervates area X which in turn innervates the DLM. DLM neurons project to the LMAN and LMAN axons innervate the RA, but exactly how the system works is not clear.

Neurons in both area X and LMAN respond vigorously to the sound of the bird’s own song, so the notion has been advanced that the anterior pathway plays an instructive role for vocal learning. The idea is that the anterior nuclei compare the song being produced by the bird with the previously memorized song, and thus these neurons influence the circuitry in the posterior nuclei to achieve accurate sound production.

As birds reach sexual maturity and the period of vocal learning closes, neurons in all four of the forebrain nuclei involved in birdsong have been shown to bind and accumulate testosterone. As this happens, the density of dendritic spines on LMAN neurons decreases and the size of the LMAN nucleus regresses substantially. It may be that the instructive role of the LMAN is lost when sexual maturity is reached, triggered perhaps by the increase in testosterone and other steroid hormones, although this point remains controversial.

Other aspects of the HVC and RA nuclei are worth noting. For example, these nuclei are much larger in males than in females (up to five times larger in male canaries than in females). However, injection of testosterone into female canaries significantly increases the size of the nuclei. Finally, nuclei size in males appears to relate to singing skill — the larger the nuclei, the better the singer.

Now that specific groups of cells involved in sound production and vocal learning for birdsong are identified, it will be possible to work out the circuitry of the sound production and vocal learning areas and to uncover how the circuitry is being modified during development. Already some observations are pertinent. For example, axons from the LMAN are the first to innervate the RA, and only as the birds begin to sing (in this case, zebra finches) axons from the HVC enter the RA and make synapses. A guess is that the early connections from the LMAN to RA shape the HVC to RA connections, but how this might come about is unclear.

Another direction researchers are taking is to record from individual neurons in various nuclei involved in song production and vocal learning. So, for example, neurons in HVC that innervate RA will respond to the bird’s own song but not to other birdsongs. Indeed, the neurons will not respond if the song is played in reverse. Individual neurons are strongly activated by specific features of a song, but those features must occur in the context of the entire song.

Sound Localization in Owls

Studies of birdsong tell us much about song memorization and vocal learning and something of sound production. Another model system, sound localization in owls, is also highly modifiable during development and has provided further insights into issues of critical periods and how neurons and circuitry might be modified by experience.

Owls are exceptionally good at localizing sounds in space. They do this in two ways: by comparing the activation times of their two ears by a sound—intraaural timing differences—and by evaluating sound intensity differences impinging on each ear. They then construct a map of auditory space in the brain that is aligned with a map of visual space. This system enables the owl to orient its head and eyes toward an auditory stimulus. Unlike us, owls cannot move their eyes readily, so precise head positioning is crucial for auditory and visual space alignment. The auditory and visual information is integrated in the tectum, the midbrain structure that mainly receives input from the retinal ganglion cells in non mammalian species. When researchers record the activity of neurons in the owl tectum, certain neurons are seen to be bimodal; that is, they respond to both visual and sound stimuli. Furthermore, the neurons respond most vigorously when the sound and visual stimuli are coming from the same place. In other words, the auditory and visual receptive fields are superimposed in these neurons.

In early experiments, Eric Knudsen and his colleagues at Stanford University put earplugs in owls that reduced the intensity of sound reaching one ear. Initially, all animals made large localization errors. Adult animals never adjusted to the earplugs, but owls under the age of eight weeks at the time of plugging did. The young animals slowly compensated for the ear plugging until once again the visual and auditory maps corresponded and the owls modified how far they moved their heads in response to the auditory stimulus and could once again visualize where the sound was coming from. Interestingly, but perhaps not surprisingly, if owls with one ear plugged were deprived of vision, the compensation did not occur, indicating an instructive role for vision in the compensation process.

The converse experiments have also been done. If prisms that shift vision by 10°-20° to the right or left are put on young owls, the birds initially orient to where the sound tells them the sound source should be, but, of course, they cannot see the sound source because of the prisms. Recordings of neurons in the tectum of these owls show that the auditory and visual receptive fields no longer overlap. The visual receptive field is out of alignment with the auditory receptive field. In juvenile birds in which the prisms are kept on for six to eight weeks, the auditory receptive fields are gradually realigned with the visual receptive field. The animal does this by altering its head rotation to the sound, compensating for the prisms. Again, adult animals do not usually show this compensation, which extends to sexual maturity, or about 200-250 days in owls. Thus, the critical period for this compensation, like that for vocal learning in songbirds, is tied to sexual maturity.

Other observations have extended our understanding of the mechanisms underlying the establishment of the auditory and visual maps and their compensation. For example, if prisms are kept on young owls until they reach adulthood and are then removed, the animals recompensate; they completely recover over a period of weeks. This suggests that the original brain circuitry that results in the normal overlap of the auditory and visual receptive fields in the tectal neurons has persisted, even though it was not used and presumably was silent for all of this time. It is possible that new circuitry formed in the adult animal to account for this recovery, but this seems unlikely because of the experiments described next.

The experiments involved putting prisms on young owls until they compensated, and then removing them when the animals were still in the critical period. The animals and neurons recompensate, of course, but then the prisms are put on again when the owls are adults. Ordinarily adult owls do not compensate for visual distortion by prisms, but these owls do in a specific way. They compensate as adults for the same prisms they wore as juveniles, but not for other prisms—that is, for prisms that alter vision in the other direction or to a greater extent than the originals did.

These experiments indicate that synapses formed during the initial compensation period in the young bird persisted into adulthood and became active again. The discovery that circuitry modifications in young birds, and then not used for some time, can be reactivated in adults is of enormous interest and might have implications for teaching human youngsters. That is, circuitry established during early years, but then not used for years, might be more persistent than we generally appreciate. A personal anecdote might be pertinent here. When growing up, I played golf a lot, but then I essentially gave up the sport for about 30 years. When I took it up again, I found after some practice that I could play as well as I did 30 years earlier. Going beyond that level of play, however, has proved difficult.

What can we say about how the auditory maps realign with the visual maps following prism experience? The horizontal component of an auditory space map is constructed from timing differences in ear activation (interaural timing differences) in amidbrain nucleus, called the external nucleus of the inferior colliculus (ICX).The ICX receives its input from another midbrain nucleus, the ICC, whose neurons respond to different intraaural timing differences and which project in a topographic way to the ICX. The ICX projects to the optic tectum where it integrates the auditory and visual information. That is, for sounds immediately in front of the animal, there are no timing differences for activation of the two ears and thus this area of the ICX projects to that part of the optic tectum receiving input from neurons on the visual axis. Moving along the tectum away from the visual axis, by 20° for example, the ICX axons projecting to that part of the tectum have the appropriate intra aural timing differences.

Anatomical examination of the projections of the ICC neurons to the ICX show that the normal topographic projection is established early in development before prism experience exerts effects—before the critical period begins. Prism experience induces neurons to expand their terminal arborizations, so that they now synapse in regions of the ICX where they didn’t synapse before. It is this elaboration of axonal terminals that appears to account for the shift in the ICX space map, which is now congruent with the optic tectum visual map.

Both observations described above, that the maps realign following removal of the prisms in an adult animal and that adjustment of the map can occur in the adult if induced in the young animal, suggest that the neuronal changes induced by prism experience are additive, not subtractive, and that perhaps both new and old synapses persist, although either might be silenced for long periods. We shall come back to this idea of synapse silencing later in this forum..

Imprinting—Parent Recognition

The last example, imprinting, is quite far removed from language, birdsong, or sound localization yet it has many of the same characteristics during development. Learning to recognize one’s parents occurs very early in the lives of many animals, especially birds and mammals, and has obvious positive consequences. This process is known as filial imprinting and can involve the recognition and learning of visual, auditory, olfactory, and even gustatory cues by the infant. The learning of these cues occurs during short and defined critical periods in early postnatal life.

The classic work in this area was carried out by the ethologist Konrad Lorenz in Germany in the 1930s and 1940s. He worked mainly with birds and showed that if he alone raised geese from the time of hatching, the goslings imprinted onto him and thereafter followed him around as if he were their mother. Subsequent work by Lorenz and others showed that the critical period for imprinting is short, lasting only a few hours. In one experiment, ducks were exposed once, for only 10 minutes, to one of several male duck models that quacked. The extent of imprinting by this one exposure was evaluated five to 70 hours later by offering the ducklings a choice between the male model they had seen and a model of a female duck that also quacked. The female duck model was placed closer to the ducklings than the male model (1 foot versus 6 feet), yet a large percentage of the ducklings followed the male rather than the female, which was closer and louder.

Other experiments have extended the observations on imprinting, and again similarities were found with other types of behavioral learning. For example, if ducks are exposed to images of closely related versus non-closely related species—geese versus humans, for example, the ducks imprint on geese. Thus, as was concluded from the study of song learning in birds, there must be some innate neural circuitry that directs the learning, although it is flexible.

Imprinting on the wrong species can have long-term consequences for young birds. For example, a dove that had been imprinted on Lorenz later directed its courtship to his hand and even tried to mate with his hand when the hand was held in a certain position! Some birds imprint on inanimate objects. Chickens, for example, have been imprinted on a small bottle sitting on the back of a toy train moving around a track. But chicks, like other birds, prefer to imprint on their own species than on anything else...

An obvious next step in these experiments is to look for changes in neuronal physiology and morphology in various parts of the brain. This has been done in a few cases, and the most intriguing results were obtained from studies on guinea fowls that had been hearing imprinted. Auditory imprinting in this species results in neurons in a region of the forebrain—the medial neostriatum and hyperstriatum (MNH)—to respond strongly and specifically to the imprinting sound stimulus. Interestingly, the dendrites of the principal neurons in the MNH of birds that were imprinted have only about half as many dendritic spines as those of non imprinted animals. Since synapses are made mainly on the dendritic spines, these observations suggest that experience during the critical period causes a selective elimination of inputs to the MNH neurons. The loss of inputs might correlate with the decrease in the animal’s ability to be imprinted with other auditory stimuli.

To conclude, although we do not as yet have much in the way of firm neurobiological evidence as to what is going on during personality development including critical periods, we now have evidence that a number of systems show quite similar developmental features, indicating a commonality in underlying mechanisms. Furthermore, a number of these systems appear tractable in certain animals, so it should be possible to get at the underlying neurobiological mechanisms. I hope we have shown in this review something of how and why we have the bodies and minds we think we have, and some of their crucial features. Then even about something as basic as the human brain and nerves, we might say without irony, as did Ludwik Fleck, a bacteriologist and philosopher of science who wrote in 1935: "In science, just as in art and in life, only that which is true to culture is true to nature."


~ William Spurstowe. Englands Patterne and Duty in Its Monthly Fasts.(London, 1643),p. 21.
~ Ibid., 42.
~ Purves, D., and Lichtman, J. W. (2005), Principles of Neural Development, Sinauer Associates, Inc., Sunderland, MA.
~ Ramachandran, V. S., Proc. Natl. Acad. Sci., 90, 10413, 1993.
~ Ludwik Fleck. The Genesis and Development of a Scientific Fact, trans. Fred Bradley and Thaddeus Trenn (Chicago: University of Chicago Press, 1979), p. 35. (Published originally in German in 1935.)

über laboratorium dauernd zur Naturtreue
Posted: Wednesday, February 11, 2015 10:00:03 AM

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socratoad wrote:
Pure unadulterated silliness.

I'm not sure. Every time I've banged my head I've started talking in tongues.

All good ideas arrive by chance- Max Ernst
Posted: Wednesday, February 11, 2015 12:51:02 PM
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throught evolution the skull has many different shaoes
Posted: Wednesday, February 11, 2015 1:02:17 PM

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Craniology and phrenology are both practices that examine the conformation of the human skull; however, the two are very different. Craniology is the study of differences in shape, size and proportions among skulls from various human races. Phrenology deals with similar attributes of the skull, but attempts to relate these things to character and mental facilities. Though once believed to be a legitimate discipline, phrenology is now considered a pseudoscience.
Posted: Wednesday, February 11, 2015 3:58:31 PM

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At the mention of phrenology, I instantly thought of this common image, usually attributed to Freud.

When you make an assumption, you make an ass of u & umption! - NeuroticHellFem
Milica Boghunovich
Posted: Wednesday, February 11, 2015 4:35:39 PM
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Craniometry does not go into personality types... just deals with the physiognomy of the skull.
Phrenology sounds more interesting to read and find out about.
Posted: Wednesday, February 11, 2015 9:09:15 PM

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Took a lot of Gall to come up with such a notion.

"To read without reflecting is like eating without digesting." -- Edmund Burke
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