One would expect that developmental deficiencies similar to those found for language would exist for music. This uncommon condition, commonly known as tone deafness, has only recently been studied. According to the careful studies of Ayotte and colleagues, there are deficits not only in appreciating pitch variation but also in music memorization, singing, and rhythmicity. These authors propose that the defect in pitch perception is at the root of the other abnormalities. What is also interesting is that amusia occurs without any difficulty in the processing of speech and language, specifically, prosody and prosodic interpretation are preserved. (See Chap. 21 for a discussion of the acquired defects of musical appreciation.)
The fascinating phenomenon of absolute pitch (perfect pitch), in which an individual can identify or produce the pitch (frequency) of a sound without reference, remains incompletely understood. This unique ability appears to have a genetic basis and a genome-wide linkage analysis has implicated several loci (Theusch et al). Absolute pitch is known to be more common among speakers of tonal languages, and occurs in some individuals who have not had prior musical training (see Moulton).
A large portion of ambulatory pediatric neurology practice consists of children who are referred because of failure in school related to overactivity, impulsivity, and inattentiveness. The question often asked is whether they have an identifiable brain disease. According to Barlow, when a large number of such cases are analyzed, fully 85 percent prove to have no major signs of neurologic disease. Perhaps 5 percent are mentally subnormal and another 5 to 10 percent show some evidence of a minimal brain disorder. Many are clumsy. In the larger group without neurologic signs, the IQ is normal, although there are also cases of borderline intelligence. Boys are more often found to be hyperactive and inattentive than girls, just as they often have more trouble in learning to read and write. Dyslexia is frequently associated, as noted earlier. Girls with ADHD may have more trouble with numbers and arithmetic.
Human infants exhibit astonishing differences in amount of activity almost from the first days of life. Some babies are constantly on the move, wiry, and hard to hold; others are placid and slack as a sack of meal. Irwin, who studied motility in the neonate, found a difference of 290 times between the most and least active in terms of amount of movement per 24 h.
Once walking and running begin, children normally enter a period of extreme activity, more so than at any other period of life. The degree of activity, which varies widely from one child to another, seems not to be correlated with the age of achieving motor milestones or with motor skill at a later time.
Again, two groups of overactive children can be discerned early in life. In one, infants are constitutionally overactive from birth, sleeping less and feeding poorly; by the age of 2 years, the syndrome is obvious. In the other group, an inability to sit quietly only becomes apparent at the preschool age (4 to 6 years). Seldom do such children remain in one position for more than a few seconds, even when watching television. They are seen as fidgety, constantly in motion, and a bit wild in public places such as restaurants. Attention to any task cannot be sustained, hence the term attention-deficit hyperactivity disorder. As a rule, there is also an abnormal impulsivity and often an intolerance of all measures of restraint.
Currently, three clinical subsyndromes have been delineated: (1) combined hyperactivity, impulsivity, and inattention, which describes approximately 80 percent of affected children; (2) a predominantly inattentive syndrome; and (3) a small group that display only hyperactivity. It is also valuable to point out that a syndrome with most of the features of ADHD can be embedded in several forms of overarching cognitive and developmental delay, including in children with autistic traits. This takes on special significance in the exploration of a genetic basis for attention-deficit disorder, as noted in the following text.