Functional magnetic resonance imaging (fMRI) allows observing cerebral activity not only in separated cortical regions but also in functionally coupled cortical networks. Although moderate doses of ethanol slowdown the neurovascular coupling, the functions of the primary sensorimotor and the visual system remain intact. Yet little is known about how more complex interactions between cortical regions are affected even at moderate doses of alcohol.
Therefore the method of psychophysiological interaction (PPI) was applied to analyze ethanol-induced effects on the effective connectivity in the visuomotor system.
Fourteen healthy social drinkers with no personal history of neurological disorders or substance abuse were examined. In a test/re-test design they served as their own controls by participating in both the sober and the ethanol condition. All participants were scanned in a 3 T MR scanner before and after ingestion of a body-weight-dependent amount of ethanol calculated to achieve a blood alcohol concentration of 1.0‰. PPIs were calculated for the primary visual cortex, the supplementary motor area, and the left and right primary motor cortex using the statistical software package SPM.
The PPI analysis showed selective disturbance of the effective connectivity between different cortical areas. The regression analysis revealed the influence of the supplementary motor area on connected regions like the primary motor cortex to be decreased yet preserved.
However, the connection between the primary visual cortex and the posterior parietal cortex was more severely impaired by the influence of ethanol, leading to an uncoupled regression between these regions.
The decreased effective connectivity in the visuomotor system suggests that complex tasks requiring interaction or synchronization between different brain areas are affected even at moderate levels of alcohol.
This finding may have important consequences for determining which components of demanding tasks such as driving a car might be compromised earlier than the functions of the main cortical motor and visual areas.
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