Serotonergic Modulation of the BNST-CeA Circuit Promotes Sex Differences in Fear Learning.

Post-traumatic stress disorder (PTSD) is characterized by intense fear memory formation and is diagnosed more often in women than men. Here, we show that serotonin differentially affects fear learning and communication in the extended amygdala of male and female mice. Females showed higher sensitivity to the effects of pharmacologically increasing serotonin during auditory fear conditioning, which enhanced fear memory recall in both sexes. Optogenetic stimulation of dorsal raphe terminals in the anterior dorsal bed nucleus of the stria terminalis (adBNST) during fear conditioning increased c-Fos expression in the BNST and central nucleus of the amygdala (CeA), and enhanced fear memory recall via activation of adBNST 5-HT2C receptors in females only. Likewise, in females only, serotonin stimulation during learning enhanced adBNST-CeA high gamma (90-140Hz) synchrony and adBNST-to-CeA communication in high gamma during fear memory recall. We conclude that sex differences in the raphe-BNST-CeA circuit may increase risk of PTSD in women.

Prelimbic cortex drives discrimination of non-aversion via amygdala somatostatin interneurons.

The amygdala and prelimbic cortex (PL) communicate during fear discrimination retrieval, but how they coordinate discrimination of a non-threatening stimulus is unknown. Here, we show that somatostatin (SOM) interneurons in the basolateral amygdala (BLA) become active specifically during learned non-threatening cues and desynchronize cell firing by blocking phase reset of theta oscillations during the safe cue. Furthermore, we show that SOM activation and desynchronization of the BLA is PL-dependent and promotes discrimination of non-threat. Thus, fear discrimination engages PL-dependent coordination of BLA SOM responses to non-threatening stimuli.

Opposing Contributions of GABAergic and Glutamatergic Ventral Pallidal Neurons to Motivational Behaviors.

The ventral pallidum (VP) is critical for invigorating reward seeking and is also involved in punishment avoidance, but how it contributes to such opposing behavioral actions remains unclear. Here, we show that GABAergic and glutamatergic VP neurons selectively control behavior in opposing motivational contexts. In vivo recording combined with optogenetics in mice revealed that these two populations oppositely encode positive and negative motivational value, are differentially modulated by animal's internal state, and determine the behavioral response during motivational conflict. Furthermore, GABAergic VP neurons are essential for movements toward reward in a positive motivational context but suppress movements in an aversive context. In contrast, glutamatergic VP neurons are essential for movements to avoid a threat but suppress movements in an appetitive context. Our results indicate that GABAergic and glutamatergic VP neurons encode the drive for approach and avoidance, respectively, with the balance between their activities determining the type of motivational behavior.

The causal role of the somatosensory cortex in prosocial behaviour.

Witnessing another person's suffering elicits vicarious brain activity in areas that are active when we ourselves are in pain. Whether this activity influences prosocial behavior remains the subject of debate. Here participants witnessed a confederate express pain through a reaction of the swatted hand or through a facial expression, and could decide to reduce that pain by donating money. Participants donate more money on trials in which the confederate expressed more pain. Electroencephalography shows that activity of the somatosensory cortex I (SI) hand region explains variance in donation. Transcranial magnetic stimulation (TMS) shows that altering this activity interferes with the pain-donation coupling only when pain is expressed by the hand. High-definition transcranial direct current stimulation (HD-tDCS) shows that altering SI activity also interferes with pain perception. These experiments show that vicarious somatosensory activations contribute to prosocial decision-making and suggest that they do so by helping to transform observed reactions of affected body-parts into accurate perceptions of pain that are necessary for decision-making.