Disruption of functional connectivity of the default-mode network in alcoholism

Abstract

The default mode network (DMN) comprises brain structures maximally active at rest. Disturbance of network nodes or their connections occurs with some neuropsychiatric conditions and may underlie associated dysfunction. DMN connectivity has not been examined in alcoholism, which is marked by compromised DMN nodes and impaired spatial working memory. To test whether performance would be related to DMN integrity, we examined DMN functional connectivity using functional magnetic resonance imaging (fMRI) data and graph theory analysis. We assumed that disruption of short paths between network nodes would attenuate processing efficiency. Alcoholics and controls were scanned at rest and during a spatial working memory task. At rest, the spontaneous slow fluctuations of fMRI signals in the posterior cingulate and cerebellar regions in alcoholics were less synchronized than in controls, indicative of compromised functional connectivity. Graph theory analysis indicated that during rest, alcoholics had significantly lower efficiency indices than controls between the posterior cingulate seed and multiple cerebellar sites. Greater efficiency in several connections correlated with longer sobriety in alcoholics. During the task, on which alcoholics performed on par with controls, connectivity between the left posterior cingulate seed and left cerebellar regions was more robust in alcoholics than controls and suggests compensatory networking to achieve normal performance.

Figure 1.

Study design schematic. HC, healthy controls; ALC, alcoholics.

Figure 2.

Functional connectivity at rest using the posterior cingulate cortices as seeds. Left: control group; right: alcoholic group. P < 0.05 FDR corrected.

Figure 3.

Between-group comparison of the functional connectivity during the task with the left posterior cingulate cortex as seed. P < 0.05 FDR corrected.

Figure 4.

Regression slopes between local efficiency during the task in right cerebellar lobule III and performance for controls (top-left figure; r = 0.614, P = 0.015) and for alcoholics (top-right figure; r = 0.52, P = 0.047) and between local efficiency at rest in the left inferior cerebellar lobule VIII and performance for alcoholics (r = 0.522, P = 0.046).

Figure 5.

Regression slopes between duration of abstinence (in days) for alcoholics and local efficiency at rest of left cerebellar lobules III (left figure; r = 0.640, P = 0.010) and VIII (right figure; r = 0.538, P = 0.039).