UC Riverside

As sensory information being processed in the brain to support behaviors, top-down modulation is believed to shape sensory information based on goals. However, is the goal-relevant or goal-irrelevant sensory information modulated, at what stage is the sensory encoding modulated, and how is it modulated? During my PhD training in the Zagha Lab, I helped develop and trained more than 80 mice to perform a go/no-go selective whisker detection task in which mice learn to respond to target stimuli and ignore distractor stimuli. The first part of my PhD study is about how sensory information is encoded and transformed. In expert awake behaving mice, I recorded spiking activities of single units in whisker primary somatosensory cortex (wS1), and whisker region of primary motor cortex (wMC) to study sensory encoding along the hierarchy. Additionally, I developed the analytical approaches to characterize neuronal encoding of sensory content using neurometric-psychometric (N-P) comparisons. Through collaborations with my lab members, our work identified that for target stimuli, the sensory information is generated first in wS1, then propagate and amplified in wMC; for distractor stimuli, the sensory signal is also generated in wS1, but is largely attenuated before reaching wMC. The second part of my PhD study is about how sensory information is influenced by top-down modulation of wMC. I recorded neurons from 92 behavioral sessions and analyzed over 1400 single units activity under different behavioral contexts. For some of these sessions, I performed simultaneous optogenetic, opto tagging and/or whisker imaging. This research shows that when expert mice perform the task, wMC suppresses distractor sensory encoding in target-aligned S1, which potentially contributed to response suppression to distractor stimuli. At the level of single units, we find evidence for a specific form of gating – decorrelating target and distractor stimuli encoding in target-preferring excitatory neurons. We additionally provide evidence that this may be mediated by proactive (pre-stimulus) top-down drive onto GABAergic neurons in distractor-aligned sensory cortex. Overall, this work connects concepts from multiple levels of organization: distractor response suppression, top-down cortical signaling, sensory cortex signal propagation, and cellular inhibition. These two studies of mine provide a detailed description of sensory encoding in primary sensory cortex and its top-down modulation. Moreover, they suggest a new point of view of understanding top-down modulation of sensory encoding in sensory cortex, which will be further elaborated in the introduction chapter below.