John Assad, Ph.D.

Professor of Neurobiology

Harvard Medical School
Dept of Neurobiology, WAB 227
200 Longwood Ave
Boston, MA 02115
Telephone: 617-432-2804
Fax: 617 432-2811
E-mail: john_assad@hms.harvard.edu

The goal of my lab’s research is to understand how the primate brain controls behavior by integrating external sensory information with internal states, such as attention or motivation. The brain has an astonishing ability to flexibly link sensation and action. The same visual object may trigger different actions depending on external context or the animal’s internal needs, preferences or state of attention. My lab uses electrophysiological techniques to study the brain computations between sensory input and motor output. We have focused on three important aspects of this processing chain: 1) how visual information is transformed into a behaviorally useful form, 2) how appropriate movements are initiated at precise times, and 3) how the value of objects or goals in the environment is assigned to guide behavior. For many of these studies, my lab has focused on the parietal cortex, a part of the brain that acts as a bridge between sensation and action. We have also examined the role of the basal ganglia in movement control, an issue that is relevant for understanding movement disorders such as Parkinson’s disease, and we have studied the orbitofrontal cortex in the context of how the brain represents value.

Selected References:

• Eskandar EN and Assad JA (1999) Dissociation of visual, motor and predictive signals in parietal cortex during visual guidance.  Nature Neurosci. 2:88-93.
• Toth LT and Assad JA (2002) Dynamic coding of behaviourally relevant stimuli in parietal cortex. Nature 415:165-168.
• Eskandar EN and Assad JA (2002) Distinct nature of directional signals among parietal cortical areas during visual guidance. J. Neurophys. 88:1777-1790.
• Lee IH and Assad JA. Putaminal Activity for Simple Reactions or Self-Timed Movements. (2003) J. Neurophys. 89:2528-2537.
• Williams Z, Elfar JC, Eskandar EN, Toth LJ and Assad JA. (2003) Relationship of parietal activity to the perceived direction of ambiguous apparent motion. Nature Neurosci. 6:616-623.
• Maimon G and Assad JA (2006) Parietal area 5 and the initiation of self-timed movements vs. simple reactions. J. Neurosci. 26: 2487-2498.
• Lee IH, Seitz AM and Assad JA (2006) Activity of tonically active neurons in the monkey putamen during initiation and withholding of movement. J. Neurophys. 95:2391-2403.
• Padoa-Schioppa C and Assad JA (2006) Neurons in orbitofrontal cortex encode economic value. Nature. 441:223-226
• Maimon G and Assad JA (2006) A parietal signal for the proactive timing of action. Nature Neurosci. 9:948-955.
• Freedman DJ and Assad JA (2006) Experience-dependent representation of visual categories in parietal cortex. Nature 443:85-88.
• Padoa-Schioppa C and Assad JA (2008) The representation of economic value in the orbitofrontal cortex is invariant for changes of menu. Nature Neurosci. 11:95-102.
• Fanini A and Assad JA (2008) Direction selectivity of neurons in the macaque lateral intraparietal area. J. Neurophys. 101:289-305.
• Freedman DJ and Assad JA (2009) Distinct encoding of spatial and non-spatial information in parietal cortex. J. Neurosci. 29:5671-5680.
• Herrington TM, Masse NY, Hachmeh KJ, Smith  JET, Assad JA and Cook EP (2009) The effect of microsaccades on the correlation between neural activity and behavior in areas MT, VIP and LIP. J. Neurosci. 29:5793-5805.
• Maimon G and Assad JA (2009) Beyond Poisson: increased spike-time regularity across primate parietal cortex. Neuron. 62:426-440.