Tone of Voice and Mind : The Connections between Intonation ...

Notes
Cerebral specialization 23
1. The pathology of hemispheric asymmetry is too complex an issue to pursue here, but it
is worth noting that the normal pattern of functional asymmetry appears to be disturbed in
the major psychoses. Disturbances, particularly hyperactivity, of the right hemisphere have
been found in depression and abnormalities of the left hemisphere in schizophrenia. It remains
the case today that, unlike various minor psychiatric disorders, there is no satisfactory
animal model of the human psychoses. This is to be expected if, neurologically, the psychoses
are disorders of the uniquely-human balance of information-processing between the cerebral
hemispheres. As Crow (1997) has emphasized, schizophrenia may be the price Homo
sapiens as a species pays for utilizing an unusual – and apparently delicate – asymmetry of
hemispheric control for language functions. The complete unraveling of this complex knot
would, more than anything else, establish human psychology as a science and would imply
some measure of genuine therapy for psychotic patients who today can only be administered
palliatives without curative effects. Crow (1997, 1998, 2002) has been the major force in explicating
the evolutionary origins of this view by pursuing the genetics of schizophrenia. He
and colleagues have identified a gene transposition, present on the human X and Y chromosomes,
that (i) occurred after the separation of the chimpanzee and human lineages, (ii)
shows abnormalities in schizophrenics, and (iii) codes for a polypeptide, cadherin, which
is expressed solely in the human neocortex. The exact function of cadherin remains to be
established, but the “brain code” hypothesis outlined here implies that it is involved in the
functional asymmetry of the human brain (most likely, transforming the excitatory callosal
impulses at certain regions of association cortex into inhibitory effects – thus promoting
and/or maintaining hemispheric functional differences). The psychiatric implication of this
view of hominid evolution is that disturbance of the healthy functional asymmetry in the
normal brain is caused by a loss of the normal inhibition left-to-right and/or right-to-left.
The latter (leading to LH abnormalities) has been implicated as the mechanism underlying
auditory hallucinations (Jaynes 1976) and the former (leading to RH abnormalities) is
arguably the mechanism through which the contextual and affective disturbances occur in
schizophrenia.