|
Neuroscience
Cluster Scientific Retreat |
|
Department of Organismal Biology &
Anatomy Neural mechanisms of tactile motion integration in
primary somatosensory cortex The speed and direction of
motion of individual (one-dimensional) edges is ambiguous because information
about the motion component parallel to their orientation is not available, a
predicament known as the aperture problem. To acquire a veridical
percept of an object's direction of motion, it is often necessary to
integrate motion information across multiple stimulus contours that differ in
orientation or to rely on so-called terminators - such as end points,
corners, and intersections - whose direction of motion is unambiguous. As is
the case in vision, the somatosensory system
integrates local motion information in stimuli that comprise ambiguous local
motion cues, such as superimposed gratings (plaids), barber poles, and bar
fields but the mechanisms underlying tactile motion integration have yet to
be elucidated. In the present study, we presented gratings and plaids using
the tactile analog of a visual monitor and recorded the responses of neurons
in primary somatosensory cortex (S1) of macaques.
Some S1 neurons exhibited properties characteristic of motion integrators:
Analogous to visual "pattern" neurons observed in the middle
temporal area (MT), these neurons integrate motion cues from multiple
contours to encode the direction of the plaid. In contrast, other neurons,
similar to "component" neurons in area MT, encode the motion of
local contours. The direction signal conveyed by "pattern" neurons
matches the perceived direction of these same stimuli as measured in human
psychophysical experiments. Interestingly, the perceived direction of certain
plaids, whose veridical direction falls outside of the angle spanned by their
two component gratings, is very different when presented tactually and
visually. For tactile plaids, the perceived direction and corresponding
neuronal responses are determined by the vector average of motion signals
emanating from edges and terminators; for visual plaids, either a different
mechanism is invoked, or terminators are weighted more strongly in the
determination of perceived direction. 09/10/2009 |