Birdsong

Because language is unique to humans, its development is diffi-cult indeed impossible to study neurobiologically as can be done with the visual system by studying visually inexperienced or visually deprived animals, as discussed in Chapter 2. 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...

Conclusions And Speculations

Neurobiological studies of the developing brain provide much information on how the brain initially forms in the fetus. At first glance, we might conclude that early brain development depends strictly on nature intrinsic genetic directives and Chapter 1 appears to support this view. But it is important to recognize that environment and nurture can also play a role in early brain development. I use the term environment here and in the rest of this discussion on brain development very broadly....

Synapse Formation

When axons reach their target, they make synaptic contacts with those neurons they recognize. Synapse formation requires reciprocal interaction between growth cone and cell to be innervated. Substances released from the growth cone initiate the formation of postsynaptic structures conversely, the postsynaptic element provides signals to the growth cone to develop into a mature syn apse. Much of the information we have concerning synapse formation has come from study of the innervation of muscle...

Enriched Visual Environments

The visual system is a most convenient part of the brain for studying the development and maturation of brain structures. Neurons along the visual system can be readily activated by presenting visual stimuli to the eyes, and activity of the neurons is easily recorded. Visual stimuli to an animal can be altered in various ways to explore the effects of environment on visual development. Several important conclusions from these studies have already been noted others have not been emphasized so...

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...

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...

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 distinct systems have been identified one in the...

Retinitis Pigmentosa A Model Neurodegenerative Disease

As people age, they often lose not only cognitive function but also visual, auditory, and other sensory functions. They can gradually become isolated from other humans and the environment. A particularly devastating condition is age-related macular degeneration (AMD), which robs older people of their central vision. The macula is a specialized region of the retina having the highest density of photoreceptors. At its center is a small indented area, the fovea, which contains only cone...

Clues from Cold Blooded Animals

Although the evidence for the generation of new neurons throughout the mammalian brain is weak and controversial, the same is not true for cold-blooded vertebrates. In many fish, for example, the retina of the eye grows throughout the life of the animal. Around the retina's periphery is a marginal zone, consisting of neural stem cells that are continually dividing and generating all of the retina's five types of neurons and its major type of glial cell as shown in Figure 5-1. New retina is...

Genes and Behavior

Unequivocal examples of individual genes causing specific neurological diseases that significantly alter behaviors are now known, Huntington's disease being one (discussed in Chapter 5). A domi-nantly inherited disorder, it occurs in everyone who inherits a sufficiently defective copy of the gene. The nature of the gene defect in Huntington's disease is now understood, and the previously unexplained variation in onset and progression of the disease observed in those suffering from it appears to...

How Long Could We Live

It is common knowledge that average life expectancy has increased spectacularly in the past 100 years. In Europe and the United States, the average life span was less than 47 years in 1890 and by the 1990s it was more than 75 years. During the decade of 1968-1978, average life expectancy rose at the phenomenal rate of one month per year for all those over 50 In Japan, the figures are even more impressive by the mid-1990s the average life expectancy for women was about 83 years of age. Japanese...