Coherence between cortical regions has been implicated in cognitive functions including attention and working memory. Coherence may act to dynamically alter the routing of information through the brain, providing the flexibility that is necessary for cognition. Indeed, disruptions in coherence are linked to neural disorders such as schizophrenia and autism spectrum disorder. There has been no systematic, in vivo, study of how inter-cortical coherence arises. Here we will test the hypothesis that inter-area cortical gamma (30-80 Hz) coherence occurs when local oscillations in a source region propagate to, and synchronize with, a target region. Computational modeling predicts that the strength of pre-existing gamma in the target will affect its coherence with an incoming oscillation: 'weak'local gamma oscillations will be easily entrained, leading to coherence between the two regions, while 'strong'oscillations resist external input, making coherence difficult (unless the input matches in phase and frequency). Testing this hypothesis requires causal in vivo control of local oscillations, a technique that the Moore laboratory has recently developed utilizing optogenetics. Coupling optogenetics with multi-area recording will allow us to discover the rules of how oscillations cohere between areas. We will optogenetically induce local gamma oscillations in a source area (primary somatosensory cortex, SI) and measure their coherence with a target area (secondary somatosensory cortex, SII). We will test our hypothesis by manipulating the strength of ongoing gamma oscillations in the target in three ways.
In Aim 1, we will optogenetically induce gamma oscillations in the target, parametrically varying the power and phase, in order to determine their effect on coherence. Cholinergic agonists induce gamma oscillations in the neocortex and acetylcholine may underlie the inter-areal coherence observed in attention. Therefore, in Aim 2, we will induce gamma oscillations in the target by increasing the local cholinergic tone and measuring its impact on coherence. Rodent, monkey and human data link gamma oscillations with attention. So, in Aim 3, we will test the impact of attention on the ability to optogenetically induce local gamma, and its impact on establishing coherence between areas.
These aims will directly test an important hypothesis about the mechanism of inter-areal coherence. In addition, this proposal will allow me to learn optogenetic, electrophysiological, and behavioral techniques in mice, under the mentorship of Dr. Christopher Moore. My future career goals are to combine my previous primate experience with these new techniques in mice. I will use electrophysiology in primates trained to perform complex behaviors to generate hypotheses about the neural mechanisms underlying cognition. These proposed neural mechanisms can then be dissected using the powerful methods available in mice.
This project will investigate how brain regions achieve coherence with one another in the gamma oscillation band. Coherence is thought to aid in the communication between brain regions, and alterations in gamma expression and in inter-areal coherence are found in several mental and brain disorders, including schizophrenia and autism. Our work may, therefore, provide insight into these maladaptive changes.
|Siegel, Markus; Buschman, Timothy J; Miller, Earl K (2015) Cortical information flow during flexible sensorimotor decisions. Science 348:1352-5|
|Buschman, Timothy J; Kastner, Sabine (2015) From Behavior to Neural Dynamics: An Integrated Theory of Attention. Neuron 88:127-44|