During the first stage of the project, we developed a set of techniques and approaches that allow robust and highly reliable single-neuron optogenetic stimulation in parallel with electrophysiological recordings to reveal the input structure of single neurons in the prefrontal cortex of mice. Optogenetics is a powerful neuroscience method, but it has been limited in several domains: one is the ability to accurately inhibit the release of neurotransmitter from synaptic terminals, and the other is to perform precise single-neuron manipulations while reading out neural activity. We developed new light-activated tools that allow precise silencing of neurotransmitter release with minimal light intensity. We also created viral vectors that allow the expression of both an actuator (channelrhodopsin) and a neural activity reporter. Each one of these tools made new experiments possible, and we shared these tools widely through open-access repositories.
In the realm of synaptic connectivity mapping, we focused our efforts on the cells projecting from the prefrontal cortex to the amygdala, a brain region that is crucial for emotional processing, learning and memory. We were able to describe with great detail how these neurons interact with one another and with non-amygdala-projecting neurons, paving the way for an investigation of how these connections change over time and with behavioral experience. In the second part of the project, we developed an optical system that allows neural activity recording and simultaneous photostimulation of single neurons, or neuronal ensembles, in awake and behaving mice. With this system, we are currently studying how neural activity and synaptic connectivity evolve through the process of memory consolidation.
To understand how the prefrontal circuit processes behaviorally-relevant information, we studied the encoding of social stimuli in this circuit, revealing that prefrontal neurons are tuned to social odors, and that this tuning is degraded in a genetic mouse model of autism spectrum disorder. This led us to investigate how social behavior is regulated during early life, since this is a critical period for both the maturation of the prefrontal cortex and for the development of healthy attachment behavior. We found that oxytocin, a neurotransmitter release in the prefrontal cortex during social encounters, is critical for the behavior of mouse pups toward their mother, and that disrupting the activity of oxytocin neurons leads to selective impairment in vocal communication at these very young ages. Our ongoing work is aimed at discovering the mechanism through which vocal behavior is encoded and regulated in the prefrontal cortex.
