Overview
Our lab is interested in the neural
circuitry of the primate
visual cortex and how it relates to perception and visually guided
behavior. Our current focus is on areas of the brain that make calculations
about visual motion. In what direction is it moving? How fast? Is it really
moving with respect to its surroundings, or does it just seem to be moving
because I'm moving? The calculations that allow an animal to answer these
critical questions are performed by populations of neurons which are
anatomically organized to form a map
representing all possible directions of motion in all parts of the visual
field. Superimposed on this map is a coarser organization of neurons whose
receptive fields have differing center-surround
interactions with respect to moving stimuli. This organization consists
of slab-like clusters of cells whose receptive fields have motion opponent
surrounds and thus signal local motion contrast interdigitated
with clusters of cells whose receptive fields have additive surrounds and
thus respond best to wide-field motion (Born
& Tootell 1992; Born
2000) The neurons within these two compartments make segregated
connections to higher motion processing areas (Berezovskii
and Born 2000). We believe that these neurons are performing
calculations necessary for distinguishing self- from object-motion. If we
electrically activate a direction column within an interband
while an animal is visually tracking a moving target, the smooth pursuit
eye movements are sped up in the preferred direction of the neurons we're
stimulating. If, on the other hand, we stimulate a direction column of
wide-field neurons, the pursuit is sped up in the opposite
direction;precisely the effect that one gets if the visual background
moves in the preferred direction, which causes the target to appear as if
it's moving in the opposite direction (so-called "induced motion" Born
et al. 2000
A second major focus
of the lab concerns the integration of visual motion signals. Given that MT
neurons appear to perform some of the calculations necessary to distinguish
and object from the visual background, we might ask how different local
motion signals emanating from the same object are combined to form an
accurate representation of object motion. You can read a brief summary of
this work here. For a more detailed treatment of motion
integration see Born
& Bradley 2005.
Techniques
We use combinations of extracellular
electrophysiology, 2-deoxyglucose mapping and anatomical tracing in order
to learn the nature of the neural circuitry and the sorts of calculations
that it makes. This allows us to make predictions about what that circuit
is doing for the animal--predictions which we can test by activating parts
of the circuits electrically or inactivating them by cooling in order to
assess their role in behavior. If we have formulated our theories
correctly, we should be able to perturb the behavior in specific and
interesting ways.
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