Altered impulse control in alcohol dependence: neural measures of stop signal performance

Abstract

Background: Altered impulse control has been implicated in the shaping of habitual alcohol use and eventual alcohol dependence. We sought to identify the neural correlates of altered impulse control in 24 abstinent patients with alcohol dependence (PAD), as compared to 24 demographics matched healthy control subjects (HC). In particular, we examined the processes of risk taking and cognitive control as the neural endophenotypes of alcohol dependence.

Methods: To this end, functional magnetic resonance imaging (fMRI) was conducted during a stop signal task (SST), in which a procedure was used to elicit errors in the participants. The paradigm allowed trial-by-trial evaluation of response inhibition, error processing, and post-error behavioral adjustment. Furthermore, by imposing on the subjects to be both fast and accurate, the SST also introduced a distinct element of risk, which participants may or may not avert during the task. Brain imaging data were analyzed with Statistical Parametric Mapping in covariance analyses accounting for group disparity in general performance.

Results: The results showed that, compared to HC, PAD demonstrated longer go trial reaction time (RT) and higher stop success rate (SS%). HC and PAD were indistinguishable in stop signal reaction time (SSRT) and post-error slowing (PES). In a covariance analysis accounting for go trial RT and SS%, HC showed greater activity in the left dorsolateral prefrontal cortex than PAD, when subjects with short and long SSRT were contrasted. By comparing PAD and HC directly during stop errors (SE), as contrasted with SS, we observed greater activity in PAD in bilateral visual and frontal cortices. Compared to HC, PAD showed less activation of the right dorsolateral prefrontal cortex during PES, an index of post-error behavioral adjustment. Furthermore, PAD who showed higher alcohol urge at the time of the fMRI were particularly impaired in dorsolateral prefrontal activation, as compared to those with lower alcohol urge. Finally, compared to HC subjects, PAD showed less activity in cortical and subcortical structures including putamen, insula, and amygdala during risk-taking decisions in the SST.

Conclusion: These preliminary results provided evidence for altered neural processing during impulse control in PAD. These findings may provide a useful neural signature in the evaluation of treatment outcomes and development of novel pharmacotherapy for alcohol dependence.

Figures

Figure 1

(a) Stop signal paradigm. In “go” trials (75%) observers responded to the go signal (a circle) and in “stop” trials (25%) they had to withhold the response when they saw the stop signal (an X). In both trials the go signal appeared after a randomized time interval between 1 to 5 s (the fore-period or FP) following the appearance of the fixation point. The stop signal followed the go signal by a time delay – the stop signal delay (SSD). The SSD was updated according to a staircase procedure, whereby it increased and decreased by 64 ms following a stop success (SS) and stop error (SE) trial, respectively. (b) An example sequence of trials to illustrate the definition of post-go slowing vs. post-go speeding in go trial reaction time; and post-error slowing vs. post-error speeding in go trial reaction time.

Figure 2

Compared to healthy control subjects, patients with alcohol dependence showed less activation of the lateral prefrontal cortex during response inhibition. Color bar represents voxel T value. See text for details.

Figure 3

Compared to healthy control subjects, patients with alcohol dependence showed greater activation in a number of cortical structures during error processing. Contrast in BOLD signal was overlaid on a T1 structural image in axial sections. Orientation is neurological: R=R. These brain regions are summarized in Table 4.

Figure 4

Compared to healthy control subjects, patients with alcohol dependence showed less activation of the right dorsolateral prefrontal cortex during post-error slowing. Color bar represents voxel T value. See text for details.

Figure 5

Compared to healthy control subjects, patients with alcohol dependence showed less activation in several cortical and subcortical structures during risk taking decision in the stop signal task. Contrast in BOLD signal was overlaid on a T1 structural image in axial sections. Orientation is neurological: R=R. These brain regions are summarized in Table 5.