Erin Rich, MD, Ph.D.: Neural coding for flexible behavior in prefrontal cortex
October 10th, 2023

 Cognitive processes depend on the collective activity of populations of neurons. Together, interacting neurons produce complex dynamics that may reveal key mechanisms linking neuron firing to thought and behavior. In this talk, I will discuss our recent work investigating the rich dynamics of population activity in the prefrontal cortex. Across different tasks requiring evaluation, value-based decision-making, and working memory, neural populations reveal how cognitive processes evolve and how relevant information is structured and restructured to meet task demands. Together, these studies illustrate how population dynamics can provide important insights into neural mechanisms of cognition that are poorly captured by examining single neurons in isolation.

Paul Anastasiades, Ph.D.: Synaptic development of sensory and prefrontal circuits
September 19th, 2023

During postnatal development, the brain undergoes a series of processes that bring about its mature architecture. These include neuronal migration, apoptosis, synapse formation and maturation. The timeline of cortical maturation is thought to be hierarchical, with primary sensory areas maturing earlier than higher-order areas, such as the prefrontal cortex (PFC). The cortex is a laminar structure with distinct synaptic inputs targeting specific layers. Within each cortical area there is also evidence for layer-specific development. For example, sensory critical periods in the mouse somatosensory barrel cortex (S1BF) follow an “outside-in” pattern, occurring first in thalamo-recipient layer (L)4 followed by superficial L2/3. The maturation of the PFC is thought to be delayed to that of S1BF. However, much less is known about the timeline of this maturation, particularly with respect to the development of synaptic connectivity within specific layers. Determining this may provide insight into when different inputs or cell types undergo synapse maturation. This project aims to determine similarities and differences in the synaptic maturation of a primary sensory barrel cortex (S1BF) and the PFC. To do so we have developed a pipeline for high-throughput synaptic puncta analysis using transgenic mice that express the synaptic protein PSD-95 tagged to GFP. We will compare the maturation of synapses between layers and regions to determine both common rules and region-specific differences of synapse development between cortical areas.

Stefano Fusi, PhD: Disentangled and flexible representations in the prefrontal cortex and the hippocampus   
June 6th, 2023
The curse of dimensionality plagues models of reinforcement learning and decision-making. The process of abstraction solves this by constructing variables describing features shared by different instances, reducing dimensionality, and enabling generalization in novel situations. Stefano Fusi’s team characterized neural representations in monkeys and humans performing a task described by different hidden and explicit variables. Abstraction was defined operationally using the generalization performance of neural decoders across task conditions not used for training, which requires a particular geometry of neural representations. Neural ensembles in prefrontal cortex, hippocampus, and simulated neural networks simultaneously represented multiple variables in a geometry reflecting abstraction but that still allowed a linear classifier to decode a large number of other variables (high shattering dimensionality). Furthermore, this geometry changed in relation to task events and performance. These findings elucidate how the brain and artificial systems represent variables in an abstract format while preserving the flexibility conferred by high shattering dimensionality.

Timothy Buschman, PhD: Neural Dynamics of Cognitive Control
May 23, 2023

Cognitive control guides behavior by controlling what, where, and how information is represented in the brain. Several mechanisms have been proposed to support cognitive control, such as gain modulation or synchronizing neural activity. In this talk, Timothy Buschman will present evidence for a new mechanism of cognitive control: by dynamically transforming neural representations into and out of different ‘subspaces’, cognitive control can route information through the brain.

Jessica Cardin, PhD: State-dependent patterns of neuromodulatory signaling in the cortex
April 18, 2023

Spontaneous and sensory-evoked cortical activity is highly state-dependent, promoting the functional flexibility of cortical circuits underlying perception and cognition.  Using neural recordings in combination with behavioral state monitoring, Jessica Cardin’s team finds that arousal and motor activity have complementary roles in regulating local cortical operations, providing dynamic control of sensory encoding. They recently developed an approach for dual mesoscopic imaging of acetylcholine release and neural activity across the entire cortical mantle in behaving mice. They find spatiotemporally heterogeneous patterns of cholinergic signaling across the cortex. These findings suggest dynamic state-dependent regulation of cortical network operations at the levels of both local and large-scale circuits.

Nicholas A. Steinmetz, PhD: Large-scale electrophysiology with Neuropixels: Reproducibility and Distributed Coding
February 21, 2023

In this talk, Nicholas Steinmetz will describe the use of Neuropixels technology to make large-scale electrophysiological recordings from the brains of awake mammals. In particular, he will focus on the efforts of the International Brain Laboratory to establish the reproducibility of measurements made with Neuropixels across experimenters and across laboratories. Moreover, the results of experiments using Neuropixels to study distributed coding of vision and action across the mouse brain will be described.