Animals rely on olfaction to find food, attract mates and avoid predators. In this talk I will present some of our recent findings about how different features of an odor stimulus, such as odor identity and odor intensity, are encoded in mouse piriform cortex, and will reveal the specific roles that different elements of the neural circuit play in shaping those representations.
The association cortices atrophy in cognitive disorders such as schizophrenia and Alzheimer’s Disease, while the primary visual cortex (V1) is more resilient. What makes the association cortices so vulnerable? We have been comparing the neurons that subserve visuo-spatial working memory in the primate dorsolateral prefrontal cortex (dlPFC), to neurons in V1 that respond to visual stimuli, and have found marked differences in both neurotransmission and modulation. Neurons in V1 show classic responses: they rely heavily on AMPAR neurotransmission, and cAMP signaling enhances neuronal firing, likely by increasing glutamate release. In contrast, dlPFC neurons have little reliance on AMPAR, and instead depend on cholinergic permissive effects on NMDAR transmission. These neurons are very dependent on arousal state, and feedforward, cAMP-calcium signaling increases K+ channel opening to reduce firing, e.g. during stress. Dysregulation of cAMP-calcium signaling with advancing age leads to loss of neuronal firing and impaired working memory, as well as tau phosphorylation. Dysregulated calcium-cAMP signaling and tau hyperphosphorylation are also seen in the aging entorhinal cortex, the cortical area most vulnerable in Alzheimer’s Disease. These data show how studies of the primate cortex can help to illuminate the etiology of cognitive disorders.
Understanding how social influence shapes biological processes is a central challenge in contemporary science, essential for achieving progress in a variety of fields ranging from the organization and evolution of coordinated collective action among neurons, or animals, to the dynamics of information exchange in human societies. Using an integrated experimental and theoretical approach I will address how, and why, animals exhibit highly-coordinated collective behavior, and what this can teach us about information processing more generally. I will demonstrate new imaging and immersive virtual reality technology that allows us to reconstruct (automatically) the dynamic, time-varying sensory networks by which social influence propagates in groups. This allows us to identify, for any instant in time, the most socially-influential individuals, and to predict the magnitude of complex behavioral cascades within groups before they actually occur. By investigating the coupling between spatial and information dynamics in groups we reveal that emergent problem solving is the predominant mechanism by which mobile groups sense, and respond to complex environmental gradients. I will also reveal the critical role uninformed, or unbiased, individuals play in effecting fast and democratic consensus decision-making in collectives, and will validate these predictions with experiments involving schooling fish and wild baboons. These results are shown to transcend specific systems, and may give new insights into how individual brains come to decisions, a hypothesis I will propose, and explore (preliminarily), with ongoing experiments of individual decision-making in immersive virtual environments.
Synapses are the fundamental nodes of information transmission in the brain. The efficacy of synaptic transmission, called synaptic strength and its use-dependent changes are crucial for how the brain perceives the environment, learns and stores memories. The highly diverse synaptic strengths found in a given connection at a particular moment in the hippocampal circuit may therefore reflect varied information coding and on-going learning associated with hippocampal-dependent tasks. However, the cellular and molecular basis by which synaptic strength diversity arises, that is, how synaptic strengths are set and controlled across a synapse population remain to be clarified. We have addressed this question by examining the interaction between multiple synapses of hippocampal neurons using a combination of electrophysiology and imaging approaches. We provide evidence for a novel cellular mechanism involving glial cells in regulating the heterogeneity of synaptic strengths across inputs received by single hippocampal neurons. Our findings underscore the role for glia in orchestrating synaptic transmission properties across a synapse population.
Exposure to odors emanating from a conspecific can influence the food choice, a phenomenon called social transmission of food preference (STFP). The piriform cortex codes olfactory perceptions, while the inactivation of neurons in the nucleus accumbens triggers consumption. The neural circuit and cellular substrate of this transition from olfactory perception to value-based action however remains elusive. Here we provide evidence for synaptic plasticity in the mPFC driving the food preference.