Hemispheric Asymmetry of Development Due to Drug Exposure.

Harold W Gordon

doi:10.15761/jsin.1000162

Abstract

A previous survey of the literature of fMRI brain activation for two risk factors, impulsivity and craving, for addiction were lateralized to the right and left hemispheres respectively. Most articles reported these findings without consideration of how lateral asymmetries might be relevant to understanding the underlying factors leading to addiction. The current survey is intended to extend these observations by demonstrating hemispheric asymmetry of development due to pre-natal or adolescent/adult exposure to drugs of abuse. Articles that reported either pre-natal or adolescent/adult exposure to drugs of abuse were collected and the hemisphere of the affected structures was tabulated to determine if, and which, drugs affected more structures in one hemisphere or the other or both together. Some drugs, notably cocaine and alcohol, differentially affected left or right hemisphere structures which significantly differed depending on whether individuals were exposed prenatally or as an adolescent/adult. Cocaine tended to affect more left hemisphere structures when exposed prenatally and significantly affected more in the right when exposed as adults. Alcohol had the reverse pattern. The difference in patterns of effect between pre-natal or adult exposure was significant for both. The results in this survey demonstrate that some drugs of abuse appear to have a right/left differential effect on structures of the brain. Further investigation into the reasons for this asymmetry may provide new insights into underlying factors of drug-seeking and addiction.

Highlights

For the understanding of addiction, the differential roles played by the structures and functions of the left and right hemispheres need more study
The key questions of interest for prenatal and adolescent/adult exposure are 1) whether structures are bilaterally affected or whether structures are affected in one hemisphere more than the other, 2) if more structures are affected in one hemisphere, is it the right or left hemisphere, 3) if there is a side preference, is it the same for all drugs or is there a different pattern of asymmetry for each drug, and 4) across drugs, do the patterns of lateralized effect for prenatal exposure differ from the patterns for adolescent/adult exposure?
All drugs considered: Across all studies compiled for all drugs, together, the analysis showed no asymmetry whereby more affected structures were distributed among bilateral, right and left hemispheres