Colloquium on Brain and Cognition with Mathew Diamond, PhD, SISSA

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TITLE:

Neuronal algorithms for extracting multiple percepts from a single stimulus

ABSTRACT:

When we consider the processing of a tactile stimulus, it is natural to focus on what the stimulus feels like and how the perceived features are encoded by neurons. But a second percept, explicitly or implicitly, accompanies the tactile experience – the feeling of time occupied by that stimulus. To explore the connection between stimulus perception and time perception, we begin with human and rat psychophysics. When subjects judge the duration of a vibration applied to the fingertip (human) or whiskers (rat), increasing stimulus intensity leads to increasing perceived duration. Symmetrically, increasing vibration duration leads to increasing perceived intensity. From this relationship, we build a computational framework where the vibration-evoked firing early in the processing stream is accumulated by two integrators, in parallel, each integrator giving rise to a corresponding percept (intensity and duration). This framework makes predictions for the perceptual effects – on both intensity and duration – of direct manipulation of firing in sensory cortex, which we verify by optogenetics in rats. However, just when everything begins to make sense, the story becomes more complex: a subtle change in the physical features of the tactile stimulus causes the engagement of a very different pathway for the perception of time. We conclude that the mechanisms underlying the feeling of stimulus duration are multiple and are adaptable to stimulus properties.

I am a Professor of Cognitive Neuroscience at the International School for Advanced Studies in Trieste Italy (known by its Italian acronym, SISSA). I earned a Bachelor of Science degree in Engineering from the University of Virginia in 1984 and a PhD in Neurobiology from the University of North Carolina in 1989. I was a postdoctoral fellow with Ford Ebner at Brown University and then an assistant professor at Vanderbilt University before moving to SISSA to create the Tactile Perception and Learning Laboratory in 1996. My main interest is to specify the relationship between neuronal activity and perception. The research is carried out mostly in the tactile whisker system in rodents, but some experiments attempt to generalize the principles found in the whisker system to the processing of information in the human tactile sensory system.

Outside my research activities, I am vice-Director of the university and delegate for international initiatives. I continually try to get young people interested in neuroscience through international courses; for the same reason, I co-authored the introductory book, From Neuron to Brain (5th edition, 2012; 6th edition, 2020).

Host

Mark Bear

Organizer

Brittany Greenough