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Must-Read Circuit Neuroscience of 2020: Vol. I

Posted by Sushmitha Gururaj, PhD - 03.02.2020

We're two months into 2020 and our beloved circuit neuroscience community has already served up so many treats that we're wondering if it's still the holidays! We're excited to share with you our collection of top reads of 2020 thus far. You'll find that each of them informs on fundamental biological functions and provided novel insights into neural circuitry. Happy reading! 

1. All hands on deck for motor learning!

Cortical synaptic AMPA receptor plasticity during motor learning by Richard H. Roth, Robert H. Cudmore, Han L. Tan, Ingie Hong, Yong Zhang, Richard L. Huganir. Neuron.

Sure, there are parts of the brain super specialized to perform certain functions. But this study shows that for a certain motor learning function at least, multiple brain areas including non-motor function regions are involved. Using in vivo two-photon microscopy during a forelimb reaching task (for food), Roth et al. examined mouse cortical AMPA receptor (AMPARs) activity. They found increased activity in not just the motor cortex, but in the visual cortex too, suggesting that multiple sensory cues are involved in successful motor learning. 

2. Extinguishing fear is the reward. 

Amygdala Reward Neurons Form and Store Fear Extinction Memory by Xiangyu Zhang, Joshua Kim, Susumu Tonegawa. Neuron.

During fear extinction training, mice can overcome fear memory-induced behavior by what is thought to be suppression of the fear memory with the formation of new memories. Zhang et al. present an elegant demonstration of how this happens, using the nVistaᵀᴹ miniscope. Briefly, a specific subset of posterior basolateral amygdala (pBLA) neurons expressing Ppp1r1b drive positive reward memories that override the negative valence associated with the original fear memories via Rspo2-expressing neuronal activity. The authors hope that identification of the specific neuronal subpopulation responsible for fear extinction can help treat fear disorders like PTSD and anxiety.
 
3.  Hypothetical thinking, explained.

Constant sub-second cycling between representations of possible futures in the hippocampus by Kenneth Kay, Jason E. Chung, Marielena Sosa, Margaret C. Larkin, Daniel F. Liu, Loren M. Frank. Cell. 

In this fascinating study, the authors find evidence to assign a new function to the hippocampus- imagination. Tracking of hippocampal place cell activity during exploration of a M-shaped maze revealed fast and constant switching between the animal's present location and possible future locations- left and right or forward and backward. This oscillating activity was strongest when the mouse had to make a decision, suggesting that the place cells create a menu of hypothetical scenarios from which to make a decision, based on experience or motivations like hunger, thirst, etc.  
 

As a rat moves from the center of a maze into its left pathway (right panel), neurons called place cells (shown in different colors) are active. Each vertical line (left) and dot (right) corresponds to an activity spike from a particular cell. Credit: Tom Davidson, Anna Gillespie, Loren Frank

4. Does this newly identified neural activity make humans... humans? 

Dendritic action potentials and computation in human layer 2/3 cortical neurons by Albert Gidon, Timothy Adam Zolnik, Pawel Fidzinski, Felix Bolduan, Athanasia Papoutsi, Panayiota Poirazi, Martin Holtkamp, Imre Vida, Matthew Evan Larkum. Science.

The human brain's cortical layer 2/3 (L2/3) is thicker and denser with neurons than in rodents. So does this somehow make us unique? Gidon et al. use a combination of ex vivo slice physiology, calcium imaging and computational biology to investigate L2/3 pyramidal neurons' dendritic activity and reveal previously unidentified activity dynamics. This novel activity is a type of calcium-mediated dendritic action potential (dCaAP) that, unlike other action potentials reliant on sodium and potassium ion, is transmitted via calcium ions. This form of synaptic activity has not been observed in any other mammalian neurons thus far!    

5. An unexpected brain region makes context-dependent movements.

Context-dependent decision making in a premotor circuit by Zheng Wu, Ashok Litwin-Kumar, Philip Shamash, Alexei Taylor, Richard Axel, Michael N. Shadlen. Neuron.

Often, the decision to move or not move depends on the context- moving objects around us, perceived threats, etc. In this study, the authors have identified a novel neuronal subpopulation in the anterior lateral motor cortex (ALM) as responsible! Using an olfactory delayed match to sample task where mice learned a directional licking response based on odors, layer 2 pyramidal neurons of the ALM were found to mediate the receiving of odor information to inform the licking decision. 

Hope you enjoyed reading these as much as we did.😊 Thank you for reading!

Topics: must-read publications


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