Genetic Theories

Alongside the more fanciful theories there was a growing belief that handedness is inherited. Early genetic theories that treated handedness in terms of classic Mendelian theory were abandoned when it became clear that predictions of family inheritance made by these theories were not supported by the data. In particular, if left-handedness were indeed determined by a recessive gene, then the children of two left-handed parents should not be right-handed. Data collected by Chamberlain (1928) and...

Tasks Favoring the Left Hemisphere

Birds are the most visually dependent class of vertebrates, and the statement of Rochon-Duvigneaud (1943) that a pigeon is nothing but two eyes with wings is probably valid for most avian species. Man, a highly visual primate, sees the world with the information transmitted by about 1 million fibers within each optic nerve. This is only 40 of the number of retinal axons counted in a single optic nerve of pigeons and chicks (Binggeli & Paule, 1969 Rager & Rager, 1978). The acuity of many...

The Thalamofugal Pathway

At first glance the general organization of the thalamofugal pathway seems to be similar in pigeons and chicks. However, in contrast to pigeons (Hodos et al., 1984), thalamofugal lesions affect frontal viewing in chicks importantly (Deng & Rogers, 1997). This suggests that, unlike pigeons, the frontal field is represented within the thalamofugal system in chicks. But this is not the only difference between chicks and pigeons. As will be outlined below, the organization of tecto- and...

Alan A Beaton

The large area of the human cortex devoted to representation of the hands attests to the importance of manual skill in the course of evolution, yet the two hands are rarely used with equal facility. Although right-handedness is the dominant tendency among all societies that have been studied (Harris, 1980,1990 Peters, 1995), a proportion of the population has always preferred the left hand. Variation in this proportion in different regions of the world may be due to cultural (see Payne, 1987...

Does Da Play A Causal Role In The Induction Of Stress Andor Anxiety States

The ability of environmental and pharmacological stressors to increase rates of DA neurotransmission within PFC suggests the possibility that PFC DA may provide a unique and critical contribution to the induction of anxiety and or stress states (for review, see Horger & Roth, 1996). Consistent with this hypothesis is the suppression of PFC DA neurotransmission by anxiolytic benzodiazepines. However, there are a few important additional observations that call into question either the extent...

The Role Of Learning

There seems to be little doubt that the relative frequency of left-handedness (e.g., Tambs et al., 1987 Gilbert & Wysocki, 1992 Davis & Annett, 1994 Hugdahl et al., 1996) and left-footedness (Porac, 1996 Bell & Gabbard, 2000) declines with age and now is less than it was a century ago. The reason for this is much debated, but one theory is that it represents a relaxation in recent years of cultural pressure toward obligatory use of the right hand for certain tasks (Brackenridge, 1981)....

The Testosterone Theory

Geschwind and Behan (1982) proposed that at a critical stage of prenatal brain maturation, excessively high levels of fetal male hormone, for example, testosterone, cause a slowing down in development of the left cerebral hemisphere relative to the right hemisphere in a region known as the planum temporale, part of the superior surface of the temporal lobe. The homologous region on the right side was said to grow larger to compensate for the reduction in growth of the left side. Since the...

The Development Of Avian Visual Lateralization

Embryos of virtually all avian species keep the head turned so that the right eye is exposed to light shining through the translucent shell while the left eye is occluded by the body Kuo, 1932 figure 1.7 . Since brooding parents regularly turn their eggs and often leave their nests for short time periods, the embryo's right eye has a high probability of being stimulated by light before hatching. Thus, it is conceivable that asymmetry of light stimulation is the key event leading to visual...

The Liepmann Hypothesis

The most common explanation of right-handedness is that it has something to do with a superiority of the left over the right hemisphere in motor control, as was argued by Ogle 1871 over 100 years ago. The contrary position, that development of the left hemisphere is due to preferential use of the right hand, has also been proposed Wharton, 1884 . Apraxia or dyspraxia is a term used somewhat loosely and con-fusingly to refer to disorders in planning, remembering, or executing voluntary,...