Very excited for Edward and Manuel, joint postdocs with the Tank Lab and part of our BRAIN CoGS big collaboration, who have this paper now out in Nature.

• Edward H. Nieh, Manuel Schottdorf, Nicolas W. Freeman, Ryan J. Low, Sam Lewallen, Sue Ann Koay, Lucas Pinto, Jeffrey L. Gauthier, Carlos D. Brody & David W. Tank, Geometry of abstract learned knowledge in the hippocampus, Nature 2021. 

Abstract: Hippocampal neurons encode physical variables^{1,2,3,4,5,6,7} such as space¹ or auditory frequency⁶ in cognitive maps⁸. In addition, functional magnetic resonance imaging studies in humans have shown that the hippocampus can also encode more abstract, learned variables^9,10,11. However, their integration into existing neural representations of physical variables^12,13 is unknown. Here, using two-photon calcium imaging, we show that individual neurons in the dorsal hippocampus jointly encode accumulated evidence with spatial position in mice performing a decision-making task in virtual reality^14,15,16. Nonlinear dimensionality reduction¹³ showed that population activity was well-described by approximately four to six latent variables, which suggests that neural activity is constrained to a low-dimensional manifold. Within this low-dimensional space, both physical and abstract variables were jointly mapped in an orderly manner, creating a geometric representation that we show is similar across mice. The existence of conjoined cognitive maps suggests that the hippocampus performs a general computation—the creation of task-specific low-dimensional manifolds that contain a geometric representation of learned knowledge.

We’re very excited to see this paper out! How does SC contribute to executive control? Our data suggests that the SC can be at the very heart of executive control, responsible for combining cognitive control signals with sensory inputs to compute context-appropriate responses. Remarkably, the fully context-appropriate responses can be decoded from SC neurons almost 200 ms faster than from cortical neurons (wow!), suggesting the computation may be led, and happen, in the SC itself. Circuit modeling supports this idea, with large-scale searches revealing a wide variety of possible SC circuits that would achieve this and that are compatible with the experimental data.

• Chunyu A Duan, Marino Pagan, Alex T Piet, Charles D Kopec, Athena Akrami, Alexander J Riordan, Jeffrey C Erlich, Carlos D Brody, “Collicular Circuits for Flexible Sensorimotor Routing“, Nature Neuroscience 2021.

Abstract: Context-based sensorimotor routing is a hallmark of executive control. Pharmacological inactivations in rats have implicated the midbrain superior colliculus (SC) in this process. But what specific role is this, and what circuit mechanisms support it? Here we report a subset of rat SC neurons that instantiate a specific link between the representations of context and motor choice. Moreover, these neurons encode animals’ choice far earlier than other neurons in the SC or in the frontal cortex, suggesting that their neural dynamics lead choice computation. Optogenetic inactivations revealed that SC activity during context encoding is necessary for choice behavior, even while that choice behavior is robust to inactivations during choice formation. Searches for SC circuit models matching our experimental results identified key circuit predictions while revealing some a priori expected features as unnecessary. Our results reveal circuit mechanisms within the SC that implement response inhibition and context-based vector inversion during executive control.

Congratulations to Abby Russo, who is joining many science friends at the Systems Neuroscience startup company CTRL-Labs!

Congratulations to Sue Ann Koay, who is starting up her own group at Janelia!

Sue Ann Koay, Stephan Thiberge, Carlos Brody, David Tank, “Amplitude Modulations of Cortical Sensory Responses in Pulsatile Evidence Accumulation.” eLife 2020.

How does the brain internally represent a sequence of sensory information that jointly drives a decision-making behavior? Studies of perceptual decision-making have often assumed that sensory cortices provide noisy but otherwise veridical sensory inputs to downstream processes that accumulate and drive decisions. However, sensory processing in even the earliest sensory cortices can be systematically modified by various external and internal contexts. We recorded from neuronal populations across posterior cortex as mice performed a navigational decision-making task based on accumulating randomly timed pulses of visual evidence. Even in V1, only a small fraction of active neurons had sensory-like responses time-locked to each pulse. Here, we focus on how these ‘cue-locked’ neurons exhibited a variety of amplitude modulations from sensory to cognitive, notably by choice and accumulated evidence. These task-related modulations affected a large fraction of cue-locked neurons across posterior cortex, suggesting that future models of behavior should account for such influences.

Thomas Luo*, Adrian Bondy*, Diksha Gupta, Verity Elliott, Charles Kopec, Carlos Brody, “An approach for long-term, multi-probe Neuropixels recordings in unrestrained rats”, eLife 2020

The use of Neuropixels probes for chronic neural recordings is in its infancy and initial studies leave questions about long-term stability and probe reusability unaddressed. Here, we demonstrate a new approach for chronic Neuropixels recordings over a period of months in freely moving rats. Our approach allows multiple probes per rat and multiple cycles of probe reuse. We found that hundreds of units could be recorded for multiple months, but that yields depended systematically on anatomical position. Explanted probes displayed a small increase in noise compared to unimplanted probes, but this was insufficient to impair future single-unit recordings. We conclude that cost-effective, multi-region, and multi-probe Neuropixels recordings can be carried out with high yields over multiple months in rats or other similarly sized animals. Our methods and observations may facilitate the standardization of chronic recording from Neuropixels probes in freely moving animals.

Congratulations to postdoc Athena Akrami, who has accepted a faculty position at the Sainsbury Wellcome Centre in London!!! She expects to start there in Fall 2018.

Ben Scott

Congratulations to postdoc Ben Scott, who has accepted a faculty position at Boston University!!! He expects to start there in Fall 2018.

Whoopeee!!  The Howard Hughes Medical Institute has renewed its appointment of Carlos Brody as an HHMI Investigator for another 7 years!

HHMI’s support is critical to the entire lab. The renewal is thanks to the fantastic work of everyone in the lab!

Alex Piet

Congratulations to graduate student Alex Piet, whose paper in Neural Computation is now out (link here).

In this paper Alex uses two-node attractor network models to  figure out what neural mechanisms could lead to FOF (a rat cortical region) contributing to decision-making as the lab found in Erlich et al. eLife 2015 and Erlich et al. Neuron 2011. Alex’s results point to specific mechanisms in which the FOF contributes “post-categorization” memory, and make some predictions that Alex then confirmed as correct in a post-hoc analysis of the data.