PBS Colloquia
Videos of colloquia for the Department of Psychological and Brain Sciences will be available here.
May 6, 2016
David A. Leopold
Senior Investigator on Cognitive Neurophysiology and Imaging
Laboratory of Neuropsychology at the National Institute of Mental Health
Title: Investigating the nature of high level visual specialization in the primate brain
Abstract
A prominent feature of the primate brain is the existence of several cortical areas in which neurons respond categorically to certain visual stimuli. Most notably are the so-called "face patches", defined as regions in which fMRI responses are stronger to face images than to other types of visual objects. Recent advances in our laboratory have made it possible to record longitudinally from individual neurons across weeks and months, opening the door for new types of experiments to investigate face-selective neurons. In my talk I will describe the results of several such experiments. For example, we found that visual selectivity of neurons in face patch AF, a "high-level" face patch, remain absolutely stable over a period up to a year, even during periods of intensive training on face identity. In agreement with several studies, I will show that neurons in this area are highly selective for faces -- in this case, based on the presentation of 10,000 flashed stimuli over a period of 3 weeks. However, the same population of "face cells", when measured during free viewing of a natural video, bear a less obvious relationship to faces and diversify significantly in their responses. Under these conditions, single neurons show a highly deterministic patter of spiking upon repeated presentations of the same video stimulus. However, neighboring neurons are often uncorrelated in their response time courses, reflecting a different functional specialization. I will show using a novel method, combining single-unit recordings and fMRI, that individual neurons fall into several distinct categories, each bearing a unique correlative relationship with functional networks throughout the brain.
May 8, 2014
Earl Miller
Picower Professor of Neuroscience
The Picower Institute for Learning and Memory and Department of Brain and Cognitive Sciences at the Massachusetts Institute of Technology
Title: Cognition is rhythmic
Abstract
How are some thoughts favored over others? A wealth of data at the level of single neurons has yielded candidate brain areas and mechanisms for our best understood model: visual attention. Recent work has naturally evolved toward efforts at a more integrative, network, understanding. It suggests that focusing attention arises from interactions between widespread cortical and subcortical networks that may be regulated via their rhythmic synchronization. This could extend to all cognitive processes, suggesting our brain does not operate continuously, but rather discretely, with pulses of activity routing packets of information. Such discrete cycles would provide a backbone for coordinating computations (and their results) across disparate networks. However, it comes at a cost: it's naturally limited in bandwidth; only so many things can be computed or carried in a single oscillatory cycle. This can explain the most fundamental property of conscious thought, its limited capacity, which is the reason why we evolved attention in the first place.
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