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My 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 [map_MT.html]
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 [band.html; also incorporate bimod3.jpg] 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 (interbands) interdigitated with
clusters of cells whose receptive fields have additive surrounds
and thus respond best to wide-field motion (bands) [link to references:
Born & Tootell 1992; Born 2000]. The neurons within these two
compartments make segregated connections to higher motion processing
areas [link to figure containing om66_x29_sup2.jpg and om82_connections_color.jpg;
link to 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 [rtb_local_asc.jpg, rtb_mstim_vavg.jpg
and rtb_local_mstim_kgram.jpg]. If, on the other hand, we stimulate
a direction column of wide-field neurons, the pursuit is sped up
in the opposite direction [rtb_wf_asc.jpg and rtb_wf_mstim_kgram.jpg]—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") [link
to 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. Segue to "Integrative action" riff.
Techniques: We use combinations of extracellular electrophysiology
[rtb_dirtune.jpg], 2-deoxyglucose mapping [rtb_2dg.jpg] and anatomical
tracing [rtb_tracers.jpg] 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 manipulating the circuits
electrically [mstim_method.jpg, rtb_mstim.jpg] 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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