Dept. of Neurobiology
Harvard Medical School

220 Longwood Ave.
Boston, MA 02115-5701
office: (617) 432-1307
lab: (617) 432-3962
fax: (617) 432-1639



















Goal: We seek to understand the circuitry of the mammalian cerebral cortex and how it endows us with the ability to see . . . and hear and think and talk.

Approach: We study visual cortex of alert monkeys trained to report specific aspects of their visual experience. This allows us to define the neural correlates of specific percepts and then study their underlying mechanisms by activating or inactivating components of the circuit.

Techniques: Our primary tools are extracellular electrophysiology—both with single electrodes and multi-electrode arrays—and psychophysics. They are complemented by techniques that allow us to dissect and probe cortical circuitry:


· circuit tracing with genetically modified viruses (rabies and VSV)

· cortical cooling (cryoloops) to reversibly inactivate circuit elements

· microstimulation to insert specific signals into cortical circuits

· pharmacogenetics to allow us to manipulate neurons based on where they project

Current Projects:


Probing cortico-cortical feedback. Several projects in the lab are aimed at deciphering this ubiquitous, but poorly understood, aspect of cortical connectivity. We have recently shown that feedback from V2 and V3 has a relatively selective effect on the non-classical surrounds of V1 receptive fields (Nassi et al. 2013; Nassi et al. 2014). These surrounds are critical for vision, because they allow local, feature-selective responses to be modulated by the context in which they occur. This modulation is surprisingly sophisticated, and appears well suited to reduce redundancy and create sparse representations in visual cortex via input-gain control (Trott & Born 2015).


1)      Using multi-electrode arrays and cortical cooling, we are exploring the role of feedback in creating feature-specific surround suppression (Alex Trott, PiN Graduate Student; collaboration with Dr. Steve Lomber).

2)      Using multi-contact “V-probes” to record across layers in V1 while inactivating MT with a new class of MRI-compatible cryoloops, we are testing hypotheses regarding layer-specific feedback and the role of MT feedback in generating motion-selective surround suppression (Till Hartmann, Postdoctoral Fellow).

3)      In animals trained to discriminate the orientation of noisy Gabor stimuli, we are testing the predictions of a hierarchical Bayesian model of perceptual inference. This involves recordings in V1 with multi-electrode arrays while inactivating V2 feedback (Camille Gomez-Laberge, Postdoctoral Fellow; collaboration with Dr. Ralf Haefner).

4)      Using trans-synaptically transported viruses and immunocytochemistry, we are examining how feedback interacts with local cortical circuits (Vladimir Berezovskii, Imaging Specialist; collaboration with Dr. Connie Cepko).

5)      We are developing computational models to help us understand how inactivating inputs to a region of the cortex dramatically affect neuronal variability (Camille Gomez-Laberge, Postdoctoral Fellow; collaboration with Dr. Gabriel Kreiman).



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