Brain development #2 Adam Kepacs

Adam Kepacs (Cold Spring Harbor Labs) continued his argument after the coffee break with a very specific example of the VIP inhibitory interneuron.


The cells in his diagram are identified by RNA expression pattern. Different types contact and create inhibition at different locations, e.g. distal dendritic, somatic, or axonal. VIP is shown to inhibit 75% of SOM cells, and not so much other cells.

Thus VIP activity disinhibits pyramidal cells.  And VIP gets input from local, interareal, and modulatory pathways. VIP has serotonin 5HT3 modulatory input which are ionotrropic fast receptors. And it has nACh receptors that are also fast compared with metabotropic second messenger inputs.

When you record VIP in auditory cortex, and vary tone and see that the cells are tuned to some frequency. When mouse is put in audio tone discrimination task, then, they discovered that at the moment of reward or punishment, the VIP neurons showed huge burst of activity, many sigma out of baseline, lasting ~50ms. Using wide field imaging, it turns out the vast majority are activated even in areas that have nothing to do with auditory processing, in parietal, motor, somatosensory cortex. This was bizarre, are these cells really involved in reward?

It turns out that these cells' responses are related to prediction error.  The details are currently being worked out.  But why would a cortical cell type respond to reward and punishment in the same way?

One hypothesis is that it is signaling surprise. There are different levels of surprise. The whole organism can be surprised. Or a particular stream can be surprised. Or locally, neighboring neurons could get a surprising input. System level is like reinforcement learning. At subsystem level, it could relate to supervised learning, and locally, it might be related to unsupervised learning of features.  Since the VIP modulatory inputs are fast, they could support these fast coincidence learning rules related to these different levels of learning.

The workshop then broke for snorkeling by a few and lunch by most.

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