Nature back-to-back article: Scientists find neurons that control both positive and negative emotions.

Click the blue word to focus on our prefrontal cortex, which is the most advanced cortex in the brain, is related to human learning and memory, attention regulation, reasoning and thinking, decision-making, emotion, fear memory and other advanced cognitive functions.about 70-80% of cortical neurons in mPFC are excitatory vertebral neurons, and the remaining 20-30% neurons are inhibitory interneurons. The main inhibitory neurons include somatostatin (SST positive neurons), vasoactive intestinal peptide (VIP) and small albumin inhibitory neurons (PV positive neurons) ）。from the perspective of neural projection, there are fiber connections with striatum, globus pallidus, amygdala, thalamus, hypothalamus, hippocampus, midbrain and other brain regions.it is precisely because of the complexity of this anatomy that mPFC brain regions perform many brain functions.on December 16, 2019, Nature journal Nature Neuroscience published a back-to-back article to reveal the role of SST positive neurons in mPFC brain regions in fear memory and social cognitive function, respectively.the first article was completed by Roger L. Clem, Department of neuroscience, Friedman Institute of brain research, Ikan Medical College, Mount Sinai.the expression of fear memory needs the activation of neurons in PRL region of mPFC, but the specific type of neurons is not clear.using SST CRE and PV CRE mice to record the electrophysiological activities of these neurons in PRL area after fear training, the results showed that the spontaneous excitatory postsynaptic current frequency of SST positive neurons in this area increased, but there was no such change in PV positive neurons.further using optical fiber recording system, it was found that the activity of SST positive neurons in the brain region increased significantly at the fifth stage after the foot shock and sound pairing training, and this increase of neuron activity still appeared in the similar environment after re exposure.what role does SST positive neurons in PRL play in fear memory? After fear training, the researchers used light to suppress the stiff behavior of the SST positive neurons in this brain region, which is an important indicator of fear. The more such behaviors, the more fear they show, the lower the level of rigidity.on the contrary, light activated these neurons, even without sound cues, could promote stiff behavior in mice.this indicates that SST positive neurons in PRL play a key role in the acquisition of fear memory.previous studies have shown that the frequency of PV positive neurons in mPFC brain area decreases when exposed to sound cues, which can induce stiff behavior.is there a microcircuit between these inhibitory neurons? Further using photogenetics to activate SST positive neurons significantly increased the amplitude of inhibitory postsynaptic currents in PV positive neurons, but had little effect on excitatory neurons.surprisingly, the specific activation of PV positive neurons in this brain region has a greater inhibitory effect on excitatory neurons.this indicates that SST positive neurons can strongly inhibit PV positive neurons, and PV positive neurons are more inclined to inhibit excitatory neurons, forming a single pathway inhibition microloop.in order to further confirm the role of PV positive neurons in the fear behavior regulated by SST positive neurons, the researchers found that photoinhibition of PV positive neurons after fear training could promote the rigid behavior of mice, which was similar to the effect of specific activation of SST positive neurons to promote the rigid behavior. therefore, further construction of PV Cre / SST CRE double transgenic animals can activate the two kinds of neurons at the same time after injection of light activated virus, but can not promote the rigid behavior of mice. this indicates that activation of PV positive neurons can cancel the role of SST positive neurons in promoting fear memory expression. in general, it is found that SST intermediate neurons in mPFC encode fear memory information, which may regulate the expression of fear memory through the disinhibitory effect of PV positive neurons on excitatory neurons. in another paper, the team of Italian scientist Francesco papaleo revealed that SST intermediate neurons in mPFC brain regions encode information to recognize emotional states. more and more evidences show that the balance of excitation and inhibition among neurons determines the function of cortex. the imbalance of excitability and inhibition in mPFC results in the impairment of social exploration and social ability in mice. the researchers designed a very interesting emotional state recognition experiment. The "Observer" mice could make judgments according to the emotional state of two strange mice. Specifically, one strange mouse was deprived of water for 23 hours, and was given drinking water one hour before the beginning of behavior, which was a positive emotion for the mice, called relief mice; the other mouse drank enough water within 24 hours, called "relief mice" Neutral mice. The results showed that "Observer" mice were more likely to approach relief mice (mice were also willing to accept positive energy and positive emotion companions, and so were humans, who suddenly understood why they had so few friends). so the question is, how do mice recognize emotions? Electrophysiological recordings showed that the increased firing frequency of intermediate neurons in the mPFC was associated with the recognition of emotional states. in the mPFC brain area, the most abundant intermediate neurons are PV neurons. Therefore, they injected photoinhibition virus into the mPFC brain area of PV CRE mice, which reduced the social behavior of "Observer" mice, but did not affect the preference of mice to contact with relief mice. on the contrary, photoinhibition of SST neurons did not affect the social behavior of the "Observer" mice, but the mice were not inclined to contact the release mice, which means that the mice could not recognize the positive emotional state. in addition, the researchers further activated the SST neurons, which actually promoted the "Observer" mice to be more likely to contact the relief mice. these results suggest that sstneurons in mPFC play a key role in identifying emotional states. previous studies have shown that synchronous activity of neurons plays a key role in information transmission and processing. the researchers further found that during the process of emotion recognition, the synchronization activity of SST neurons and pyramidal neurons in mPFC increased, but the increase of synchronization of SST neurons was more obvious. in conclusion, the above two articles reveal the role of sstpnergic neurons in mPFC brain regions in different scenes. They can encode both fear memory information and information state recognition information, but they may be regulated by the disinhibition of excitatory pyramidal neurons. references; Diego scheggia, Francesca manag ò, Federica Maltese, Stefania Bruni；Somatostatin interneurons in the prefrontal cortexcontrol affective state discrimination in mice； A. Cummings and Roger L. Clem，Prefrontal somatostatin interneurons encode  fear Science: a key hub for scientists to find negative emotions - cell voice in the raphe nucleus: where will the oxygen sensing field go after the Nobel Prize boom? Nature: can you switch the memory mode by pressing the on / off button of synapses? Nature Blockbuster: can fever really cure autism? The truth is not so easy to rewrite textbooks! 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