Reduced dorsolateral prefrontal cortical hemodynamic response in adult obsessive-compulsive disorder as measured by near-infrared spectroscopy during the verbal fluency task

Abstract

Background: Near-infrared spectroscopy has helped our understanding of the neurobiological mechanisms of psychiatric disorders and has advantages including noninvasiveness, lower cost, and ease of use compared with other imaging techniques, like functional magnetic resonance imaging. The verbal fluency task is the most common and well established task used to assess cognitive activation during near-infrared spectroscopy. Recent functional neuroimaging studies have shown that the orbitofrontal cortex and other brain regions, including the dorsolateral prefrontal cortex, may play important roles in the pathophysiology of obsessive-compulsive disorder (OCD). This study aimed to evaluate hemodynamic responses in the dorsolateral prefrontal cortex in patients with OCD using near-infrared spectroscopy during the verbal fluency task and to compare these with dorsolateral prefrontal cortex responses in healthy controls.

Methods: Twenty patients with OCD and 20 controls matched for age, gender, handedness, and estimated intelligence quotient participated in this study. The verbal fluency task was used to elicit near-infrared spectroscopic activation and consisted of a 30-second pre-task, followed by three repetitions of a 20-second verbal fluency task (total 60 seconds), followed by a 70-second post-task period. The near-infrared spectroscopy experiment was conducted on the same day as surveys of obsessive-compulsive symptoms, depression, and anxiety. Z-scores for changes in the concentration of oxygenated hemoglobin were compared between the OCD patients and controls in 14 channels set over the left and right dorsolateral prefrontal cortex and frontopolar areas.

Results: During the verbal fluency task, significant task-related activation was detected in both the OCD group and the controls. Changes in oxygenated hemoglobin concentration in the right dorsolateral prefrontal cortex were significantly smaller in the OCD group than in the controls, but were not statistically significant after correction for multiple comparisons.

Conclusion: Patients with OCD have reduced prefrontal, especially right dorsolateral prefrontal, cortical hemodynamic responses as measured by near-infrared spectroscopy during the verbal fluency task. These results support the hypothesis that the dorsolateral prefrontal cortex plays a role in the pathophysiology of OCD.

Keywords: dorsolateral prefrontal cortex; functional neuroimaging; near-infrared spectroscopy; obsessive-compulsive disorder; prefrontal hemodynamic response; verbal fluency task.

Figure 1

Grand-average waveforms of changes in oxygenated hemoglobin concentration in controls (red line) and the group with obsessive-compulsive disorder (blue line). The areas enclosed with red frames show the regions of interest. The x-axis shows time course (s) and the y-axis shows the change in oxygenated hemoglobin concentration (mM • cm). Grand-average waveforms of changes in oxygenated hemoglobin concentration in healthy controls increased during the task period, but did not increase markedly in the obsessive-compulsive disorder group. Abbreviation: CH, channel.

Figure 2

Localization matrices mapped over a standard brain template. Areas shown in yellow represent matrix of guidance channels. (A) Matrix of guidance in which areas shown in orange represent regions of interest. (B) Patients with obsessive-compulsive disorder had significantly smaller changes in oxygenated hemoglobin concentration than controls at channel 18 (orange), localized near the right lateral prefrontal region.

Figure 3

Mean z-score during the verbal fluency task in the right dorsolateral prefrontal cortex (channel 18). The vertical bars represent the standard error. The oxygenated hemoglobin concentration in patients with obsessive-compulsive disorder at the right dorsolateral prefrontal cortex was significantly smaller than that in controls (P < 0.05). Abbreviations: DLPFC, dorsolateral prefrontal cortex; HC, healthy controls; OCD, obsessive-compulsive disorder; CH, Channel.