Many voxel-based morphometry (VBM) studies have found abnormalities in gray matter density (GMD) in obsessive-compulsive disorder (OCD). Here, we performed a quantitative meta-analysis of VBM studies contrasting OCD patients with healthy controls (HC). A literature search identified 10 articles that included 343 OCD patients and 318 HC. Anatomic likelihood estimation meta-analyses were performed to assess GMD changes in OCD patients relative to HC. GMD was smaller in parieto-frontal cortical regions, including the supramarginal gyrus, the dorsolateral prefrontal cortex, and the orbitofrontal cortex, and greater in the basal ganglia (putamen) and the anterior prefrontal cortex in OCD patients relative to HC. No significant differences were found between children and adults. Our findings indicate differences in GMD in parieto-frontal areas and the basal ganglia between OCD patients and HC. We conclude that structural abnormalities within the prefrontal-basal ganglia network are involved in OCD pathophysiology.

Functional and connectivity changes in corticostriatal systems have been reported in the brains of patients with obsessive–compulsive disorder (OCD); however, the relationship between basal ganglia activity and OCD severity has never been adequately established. We recently showed that deep brain stimulation of the subthalamic nucleus (STN), a central basal ganglia nucleus, improves OCD. Here, single-unit subthalamic neuronal activity was analysed in 12 OCD patients, in relation to the severity of obsessions and compulsions and response to STN stimulation, and compared with that obtained in 12 patients with Parkinson's disease (PD). STN neurons in OCD patients had lower discharge frequency than those in PD patients, with a similar proportion of burst-type activity (69 vs 67%). Oscillatory activity was present in 46 and 68% of neurons in OCD and PD patients, respectively, predominantly in the low-frequency band (1–8 Hz). In OCD patients, the bursty and oscillatory subthalamic neuronal activity was mainly located in the associative–limbic part. Both OCD severity and clinical improvement following STN stimulation were related to the STN neuronal activity. In patients with the most severe OCD, STN neurons exhibited bursts with shorter duration and interburst interval, but higher intraburst frequency, and more oscillations in the low-frequency bands. In patients with best clinical outcome with STN stimulation, STN neurons displayed higher mean discharge, burst and intraburst frequencies, and lower interburst interval. These findings are consistent with the hypothesis of a dysfunction in the associative–limbic subdivision of the basal ganglia circuitry in OCD's pathophysiology.

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When a subject faces conflicting situations, decision-making becomes uncertain. The human dorsal anterior cingulate cortex (dACC) has been repeatedly implicated in the monitoring of such situations, and its neural activity is thought to be involved in behavioral adjustment. However, this hypothesis is mainly based on neuroimaging results and is challenged by animal studies that failed to report any neuronal correlates of conflict monitoring. This discrepancy is thought be due either to methodological or more fundamental cross-species differences. In this study, we eliminated methodological biases and recorded single-neuron activity in monkeys performing a Stroop-like task. We found specific changes in dACC activity during incongruent trials but only in a small subpopulation of cells. Critically, these changes were not related to reaction time and were absent before any incorrect action was taken. A larger fraction of neurons exhibited sustained activity during the whole decision period, whereas another subpopulation of neurons was modulated by reaction time, with a gradual increase in their firing rate that peaked at movement onset. Most of the neurons found in these subpopulations exhibited activity after the delivery of an external negative feedback stimulus that indicated an error had been made. These findings, which are consistent with an executive control role, reconcile various theories of prefrontal cortex function and support the homology between human and monkey cognitive architectures.

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Doubt, and its behavioural correlate, checking, is a normal phenomenon of human cognition that is dramatically exacerbated in obsessive-compulsive disorder. We recently showed that deep brain stimulation in the associative-limbic area of the subthalamic nucleus, a central core of the basal ganglia, improved obsessive-compulsive disorder. To understand the physiological bases of symptoms in such patients, we recorded the activity of individual neurons in the therapeutic target during surgery while subjects performed a cognitive task that gave them the possibility of unrestricted repetitive checking after they had made a choice. We postulated that the activity of neurons in this region could be influenced by doubt and checking behaviour. Among the 63/87 task-related neurons recorded in 10 patients, 60% responded to various combinations of instructions, delay, movement or feedback, thus highlighting their role in the integration of different types of information. In addition, task-related activity directed towards decision-making increased during trials with checking in comparison with those without checking. These results suggest that the associative-limbic subthalamic nucleus plays a role in doubt-related repetitive thoughts. Overall, our results not only provide new insight into the role of the subthalamic nucleus in human cognition but also support the fact that subthalamic nucleus modulation by deep brain stimulation reduced compulsive behaviour in patients with obsessive-compulsive disorder.

The angle of the jaw is innervated by the auricular branch of the superficial cervical plexus (SCP). Cervical cutaneous nerves of the CP carry the sensation from the antero-lateral cervical skin. It is clinically relevant to identify the cervical cutaneous nerve distribution and the nerve point using superficial landmarks but published studies describing the emerging patterns and cervical cutaneous nerve branch distributions in the mandible are rare. The overlap between the cervical and trigeminal and facial nerve distributions and anastomoses is highly variable. The objective of this study was to characterize the distribution of the SCP nerves in the different parts of the mandible. Two hundred and fifty fresh and formalin-fixed human cadaver heads were microdissected to observe the distribution of the transverse cervical (TCN) and great auricular (GAN) nerves. Two main groups (G1 and G2) based on the emergence of the TCN and GAN behind the posterior edge of the sternocleidomastoid muscle and three types (T1, T2, and T3) based on their distribution in the different mandibular parts were observed. Statistical analysis showed that parameters related to the mandibular side (P = 0.307), gender (P = 0.218), and group (P = 0.111) did not influence the facial distribution of these nerves. The only parameter influencing the distribution was the type of nerve (GAN and TCN) (P < 0.001). In the face, the SCP reached the mandible in 97% of cases, its distribution and extent were subject-dependent. These results confirmed that the SCP could supply accessory innervation to the mandible through the TCN.