Michael Stryker to deliver Pepose Vision Sciences Award Lecture on March 12

This year’s Pepose Award in Vision Sciences, funded by an endowment from Brandeis graduates Jay Pepose (’75) and his wife, Susan Feigenbaum (’74), will be awarded to Michael Stryker, the William Francis Ganong Professor of Physiology at UCSF.  Dr. Stryker, who has been a faculty member at ‘SF since 1978, has been at the forefront of vision research for decades.  His lab has used a variety of animal models to probe cortical development and plasticity in the visual system, and developed a variety of techniques to analyze and measure these changes, often resulting in images that are visually inspiring in their own right (Figure, below).

This top down view of cat visual cortex shows color coded orientation columns, using a continuous-periodic imaging paradigm developed in the Stryker lab.

As a postdoc at Harvard Medical School, Dr. Stryker worked with Nobel Laureates Torsten Wiesel and David Hubel, whose groundbreaking research using the visual cortex of cats provided a first glimpse into cortical organization, development, and plasticity.  By studying how the responsiveness of neurons in visual cortex changes as a result of visual deprivation, Hubel and Wiesel pioneered a model for developmental neurobiology and introduced us to concepts like ocular dominance, orientation columns, and critical periods, a foundation upon which Dr. Stryker has built much in the subsequent decades: describing the arrangement of orientation maps in pinwheels; probing the role of spontaneous retinal activity in producing these maps; highlighting the importance of ongoing developmental activity using visual deprivation and pharmacological activity blockades; and more recently examining the molecular substrates of these changes using the genetically accessible murine model.  His career spans the visual field from its foundational work to the most modern, and with no end in sight!

Join us on March 12, 3:45 pm in Gersetnzang 121 as he accepts the award and delivers a public lecture on “Rewiring the Brain: Mechanisms of Competition and Recovery of Function in the Mammalian Cortex“.

A biologically plausible transform for visual recognition

People can recognize objects despite changes in their visual appearance that stem from changes in viewpoint. Looking at a television set, we can follow the action displayed on it even if we don’t look straight at it, if we sit closer than usual, or if we are lying sideways on a couch. The object identity is thus invariant to simple transformations of its visual appearance in the 2-D plane such as translation, scaling and rotation. There is experimental evidence for such invariant representations in the brain, and many competing theories of varying biological plausibility that try to explain how those representations arise. A recent paper detailing a biologcally plausible algorithmic model of this phenomenon is the result of a collaboration between Brandeis Neuroscience graduate student Pavel Sountsov, postdoctoral fellow David Santucci and Professor of Biology John Lisman.

Many theories of invariant recognition rely on the computation of spatial frequency of visual stimuli using the Fourier transform. This, however, is problematic from a biological realism standpoint, as the Fourier transform requires the global analysis of the entire visual field. The novelty of the model proposed in the paper is the use of a local filter to compute spatial frequency. This filter consists of a detector of pairs of parallel edges. It can be implemented in the brain by multiplicatively combining the activities of pairs of edge detectors that detect edges of similar orientations, but in different locations in the visual field. By varying the separation of the receptive fields of those detectors (thus varying the separation of the detected edges), different spatial frequencies can be detected. The model shows how this type of detector can be used to build up invariant representations of visual stimuli. It also makes predictions about how the activity of neurons in higher visual areas should depend on the spatial frequency content of visual stimuli.

Sountsov P, Santucci DM, Lisman JE. A Biologically Plausible Transform for Visual Recognition that is Invariant to Translation, Scale, and Rotation. Frontiers in computational neuroscience. 2011;5:53.

Pay attention!

“Pay attention!” That is often very good advice, but sometimes the advice is hard to obey.   The brain’s limited attentional resources can be overwhelmed when attention has to be distributed among multiple objects.  And the challenge is even greater when the objects are moving.  For example, imagine that you’re driving on Route 128 at rush hour.  You must attend not only to your own car’s path, but also to the whims and surprising behaviors of the cars all around you.   Working in my lab, Heather Sternshein and Yigal Agam, two PhD students in the Neuroscience Program, developed a novel electroencephalographic (EEG) technique to study how selective attention is apportioned in a task that can be described as “Route 128-on Sterioids.”   We were especially interested in the neural correlates of failures of attention, the kind of failure that, on the road, might have serious consequences.

Subjects in our experiment watched as ten identical black discs moved about randomly on a computer display for ten seconds.  The hard part was to keep track the entire time of particular, pre-designated target discs –either three, four or five.  Because all ten moving discs were identical, there were no physical features to distinguish target from non-target discs.  At the end of eight seconds, all discs came to standstill, and a subject tried to identify the discs that he or she had been tracking.  The task required attentive tracking of a subset of identical multiple moving objects, something even more challenging than navigating Route 128 at rush hour.

Every once in a while during the eight-second tracking period, one of the ten discs flashed brightly for 100 msec.  Sometimes, the flashed disc was a target disc, that is, one the subject was trying to track; sometimes the flashed disc was a non-target disc, that is, one that the subject could be ignoring.   The flash evoked a response in the subject’s brain, and our EEG system picked up that response from the subject’s scalp.  Knowing that the evoked response would be larger if the flash were delivered to an object that was being attended,  we used responses to target and non-targets as an index of how attention was distributed among the multiple moving objects.  We focused our analysis on electrodes located over occipital and parietal lobes, toward the brain’s posterior.

As expected, the relative sizes of responses to the two kinds of stimuli differed: on average, flashes on target discs evoked larger responses than flashes on non-target discs.  This difference confirmed that on average subjects were paying more attention to targets than to non-targets. But as the number of discs that had to be tracked increased —from three to four to five– subjects found the task increasingly harder, and made more errors when they had to identify the discs that they had been trying to track.  The EEG revealed the neural correlate of these failures of attention.  The difference between evoked responses to flashed targets and flashed non-targets decreased as the number of targets increased.  This shrinking difference between the two sets of neural responses could explain the systematic increase in errors as the the number of targets increased.  As additional items have to be kept track of, it becomes harder for subjects to apportion attentional resources in a way that preserves a sufficient advantage for targets over non-targets.  As a result, subjects make more errors –mistaking non-targets for targets.

We plan to adapt this basic experimental strategy to study the neural basis of attention in various groups whose performance on our task is likely to abnormal:  older adults (who show impaired behavioral performance) and habitual video-game players (who show far-better-than normal performance).  Yigal Agam is now at MGH’s Martinos Center; Heather Sternshein is in the Department of Neurobiology, Harvard University.

Sternshein H, Agam Y, Sekuler R. EEG Correlates of Attentional Load during Multiple Object Tracking. PLoS One. 2011;6(7):e22660..

Claude Desplan to speak in Bauer Distinguished Lecturer Series

Claude Desplan, Silver Professor and Professor of Biology at NYU, will visit Brandeis the week of March 21-25 as part of the M.R.Bauer Foundation Distinguished Lecturer Series. Desplan’s work focuses on developmental biology in insects, and is particularly concerned with pattern formation. A recent topic of interest is the development of the neural network that supports color vision in the optic lobe of the fruit fly.

Desplan will speak on Monday, March 21 at 4:00 pm in Gerstenzang 121. The title of his talk will be “Processing of Color Information in Drosophilia”. Desplan will speak again at Neurobiology Journal Club on March 22 at 12:05 pm in Gerstenzang 121.

According to a post at ratemyprofessors.com:

Desplan is the funniest, nicest guy ever. At first you may not be able to understand him too too easily due to his french accent but after a few days that’s not a problem. Desplan went pretty slow and went over concepts that people didn’t seem to understand. Even then he held very helpful review sessions. Great professor.


Undergraduate Biology Lab Students All Get Cataracts

After a series of renovations and modifications, the fall semester of introductory biology (Biol18b) is now an 11 week project-based lab course focused on Molecular and Structural Biology.  Students in the course now design their own mutant of γD crystallin (a human protein implicated in congenital and age-onset cataractogenesis) using site-directed mutagenesis, purify and express their protein, and then study its stability using fluorescence and AFM.

A new paper in CBE – Life Sciences Education by Brandeis undergraduates Dan Treacy, Rebecca Miller, Stefan Isaac, Danielle Saly, and Saumya Sankaran, together with grad student Susannah Gordon-Messer and Assistant Professor of Biology Melissa Kosinski-Collins,  discusses a two-year study focused on assessing both student perception of the course and analyzing the levels conceptual understanding and knowledge retention of participants.  This paper marks the second in a series of articles highlighting studies performed by life science undergraduates enrolled in an educational internship course (Ed92a) with Kosinski-Collins.

Schiller to Receive Pepose Vision Sciences Award

Peter Schiller of the Department of Brain and Cognitive Science at MIT has been selected to receive the Jay Pepose ’75 Award in Vision Sciences for 2011 from Brandeis University. Schiller is being honored for work on visual perception and neural control of guided eye movements. Schiller will visit Brandeis on March 14, 2011 to receive the award and to lecture on “Parallel Information Processing Channels Created in the Retina”. The lecture will be held at 4:00 pm in Gerstenzang 121. For more information about Dr. Schiller and the Pepose Award, please the story on Brandeis NOW.

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