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Abstract
Data recently published as indicating little or no evidence of neurotransmitter asymmetries
in post-mortem human brain were analyzed by correlational and Chi-square procedures.
Although handedness data were not available and it was not possible to determine the
functional significance of asymmetries, our analysis shows that asymmetries in several
brain structures and transmitter systems do indeed exist. The major findings are:
(1) correlations of left-right asymmetries between and within structures and transmitters
yielded a non-random distribution of significant correlations; (2) left-right asymmetries
in glutamic acid decarboxylase (GAD) and gamma-aminobutyric acid (GABA) were positively
correlated in all 9 structures examined; (3) correlations between left-right asymmetries
of different neurotransmitters within the same structure tended to be positive whereas
correlations between different structures tended to be negative: both trends were
significant; (4) choline acetyltransferase (ChAT) and dopamine (DA) were both significantly
left-biased, by Chi-square tests, in globus pallidus; left-right asymmetries in ChAT
and DA were positively correlated in globus pallidus, as well as in caudate nucleus
and putamen; (5) left-right asymmetries in ChAT and GAD were positively correlated
in all cortical areas and negatively correlated in all nigrostriatal structures; (6)
in caudate, putamen and globus pallidus, there was a significant trend for brains
with lower dopamine levels to be left-biased and vice-versa; (7) there was a highly
significant inverse correlation of age with the absolute asymmetry in globus pallidus
ChAT; (8) correlations of absolute asymmetries between the same or different neurotransmitters
in different structures were usually positive, indicating that a greater or lesser
degree of asymmetry probably characterizes each particular brain; (9) lastly, there
were several similarities between the human data and those previously reported in
rats, demonstrating that studies in the rat may reveal mechanisms and functions of
brain asymmetry that are relevant to man.