Lateral asymmetry of neurotransmitters in human brain

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.