Resting-state brain network features associated with short-term skill learning ability in humans and the influence of N-methyl-d-aspartate receptor antagonism.

Graph theoretical functional magnetic resonance imaging (fMRI) studies have demonstrated that brain networks reorganize significantly during motor skill acquisition, yet the associations between motor learning ability, brain network features, and the underlying biological mechanisms remain unclear. In the current study, we applied a visually guided sequential pinch force learning task and graph theoretical analyses to investigate the associations between short-term motor learning ability and resting-state brain network metrics in 60 healthy subjects. We further probed the test-retest reliability (n = 26) and potential effects of the N-methyl-d-aspartate (NMDA) antagonist ketamine (n = 19) in independent healthy volunteers. Our results show that the improvement of motor performance after short-term training was positively correlated with small-worldness (p = 0.032) and global efficiency (p = 0.025), whereas negatively correlated with characteristic path length (p = 0.014) and transitivity (p = 0.025). In addition, using network-based statistics (NBS), we identified a learning ability-associated (p = 0.037) and ketamine-susceptible (p = 0.027) cerebellar-cortical network with fair to good reliability (intraclass correlation coefficient [ICC] > 0.7) and higher functional connectivity in better learners. Our results provide new evidence for the association of intrinsic brain network features with motor learning and suggest a role of NMDA-related glutamatergic processes in learning-associated subnetworks.

Differing amygdala responses to facial expressions in children and adults with bipolar disorder.

OBJECTIVE: Child and adult bipolar patients show both behavioral deficits in face emotion processing and abnormal amygdala activation. However, amygdala function in pediatric relative to adult bipolar patients has not been compared directly. The authors used functional MRI to compare amygdala activity during a face processing task in children and adults with bipolar disorder and in healthy comparison subjects. METHOD: Amygdala responses to emotional facial expressions were examined in pediatric (N=18) and adult (N=17) bipolar patients and in healthy child (N=15) and adult (N=22) volunteers. Participants performed a gender identification task while viewing fearful, angry, and neutral faces. RESULTS: In response to fearful faces, bipolar patients across age groups exhibited right amygdala hyperactivity relative to healthy volunteers. However, when responses to all facial expressions were combined, pediatric patients exhibited greater right amygdala activation than bipolar adults and healthy children. CONCLUSIONS: Amygdala hyperactivity in response to fearful faces is present in both youths and adults with bipolar disorder. However, compared with bipolar adults and healthy child volunteers, pediatric bipolar patients showed amygdala hyperactivity in response to a broad array of emotional faces. Thus, abnormal amygdala activation during face processing appears to be more pervasive in children than in adults with bipolar disorder. Longitudinal studies are needed to elucidate the mechanisms of this developmental difference, thus facilitating developmentally sensitive diagnosis and treatment.