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MT studies


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Science. 1992 Feb 28;255(5048):1141-3.

Form-cue invariant motion processing in primate visual cortex.

Albright TD.

Salk Institute for Biological Studies, La Jolla, CA 92186.
The direction and rate at which an object moves are normally not correlated with
the manifold physical cues (for example, brightness and texture) that enable it
to be seen. As befits its goals, human perception of visual motion largely
evades this diversity of cues for image form; direction and rate of motion are
perceived (with few exceptions) in a fashion that does not depend on the
physical characteristics of the object. The middle temporal visual area of the
primate cerebral cortex contains many neurons that respond selectively to motion
in a particular direction and is an integral part of the neural substrate for
perception of motion. When stimulated with moving patterns characterized by one
of three very diverse cues for form, many middle temporal neurons exhibited
similar directional tuning. This lack of sensitivity for figural cue
characteristics may allow the uniform perception of motion of objects having a
broad spectrum of physical cues.
Vis Neurosci. 1989;2(2):177-88.

Centrifugal directional bias in the middle temporal visual area (MT) of the

Albright TD.

Department of Psychology, Princeton University.
We have examined the distribution of preferred directions of motion for neurons
in the middle temporal visual area (MT) of the macaque. We found a marked
anisotropy favoring directions that are oriented away from the center of gaze.
This anisotropy is present only among neurons with peripherally located
receptive fields. This peripheral centrifugal directionality bias corresponds
well to the biased distribution of motions characteristic of optic flow fields,
which are generated by displacement of the visual world during forward
locomotion. The bias may facilitate the processing of this common form of visual
stimulation and could underlie previously observed perceptual anisotropies
favoring centrifugal motion. We suggest that the bias could arise from exposure
of modifiable cortical circuitry to a naturally occurring form of selective
visual experience.
Exp Brain Res. 1987;65(3):582-92.

Local precision of visuotopic organization in the middle temporal area (MT) of
the macaque.

Albright TD, Desimone R.
The representation of the visual field in the middle temporal area (MT) was
examined by recording from single neurons in anesthetized, immobilized macaques.
Measurements of receptive field size, variability of receptive field position
(scatter) and magnification factor were obtained within the representation of
the central 25 degree. Over at least short distances (less than 3 mm), the
visual field representation in MT is surprisingly orderly. Receptive field size
increases as a linear function of eccentricity and is about ten times larger
than in V1 at all eccentricities. Scatter in receptive field position at any
point in the visual field representation is equal to about one-third of the
receptive field size at that location, the same relationship that has been found
in V1. Magnification factor in MT is only about one-fifth that reported in V1
within the central 5 degree but appears to decline somewhat less steeply than in
V1 with increasing eccentricity. Because the smaller magnification factor in MT
relative to V1 is complemented by larger receptive field size and scatter, the
point-image size (the diameter of the region of cortex activated by a single
point in the visual field) is roughly comparable in the two areas. On the basis
of these results, as well as on our previous finding that 180 degrees of axis of
stimulus motion in MT are represented in about the same amount of tissue as 180
degrees of stimulus orientation in V1, we suggest that a stimulus at one point
in the visual field activates at least as many functional "modules" in MT as in V1.
J Neurophysiol. 1984 Dec;52(6):1106-30.

Direction and orientation selectivity of neurons in visual area MT of the

Albright TD.
We recorded from single neurons in the middle temporal visual area (MT) of the
macaque monkey and studied their direction and orientation selectivity. We also
recorded from single striate cortex (V1) neurons in order to make direct
comparisons with our observations in area MT. All animals were immobilized and
anesthetized with nitrous oxide. Direction selectivity of 110 MT neurons was
studied with three types of moving stimuli: slits, single spots, and random-dot
fields. All of the MT neurons were found to be directionally selective using one
or more of these stimuli. MT neurons exhibited a broad range of direction-tuning
bandwidths to all stimuli (minimum = 32 degrees, maximum = 186 degrees, mean =
95 degrees). On average, responses were strongly unidirectional and of similar
magnitude for all three stimulus types. Orientation selectivity of 89 MT neurons
was studied with stationary flashed slits. Eighty-three percent were found to be
orientation selective. Overall, orientation-tuning bandwidths were significantly
narrower (mean = 64 degrees) than direction-tuning bandwidths for moving
stimuli. Moreover, responses to stationary-oriented stimuli were generally
smaller than those to moving stimuli. Direction selectivity of 55 V1 neurons was
studied with moving slits; orientation selectivity of 52 V1 neurons was studied
with stationary flashed slits. In V1, compared with MT, direction-tuning
bandwidths were narrower (mean = 68 degrees). Moreover, V1 responses to moving
stimuli were weaker, and bidirectional tuning was more common. The mean
orientation-tuning bandwidth in V1 was also significantly narrower than that in
MT (mean = 52 degrees), but the responses to stationary-oriented stimuli were of
similar magnitude in the two areas. We examined the relationship between optimal
direction and optimal orientation for MT neurons and found that 61% had an
orientation preference nearly perpendicular to the preferred direction of
motion, as is the case for all V1 neurons. However, another 29% of MT neurons
had an orientation preference roughly parallel to the preferred direction. These
observations, when considered together with recent reports claiming sensitivity
of some MT neurons to moving visual patterns (39), suggest specific neural
mechanisms underlying pattern-motion sensitivity in area MT. These results
support the notion that area MT represents a further specialization over area V1
for stimulus motion processing. Furthermore, the marked similarities between
direction and orientation tuning in area MT in macaque and owl monkey support
the suggestion that these areas are homologues.
J Neurophysiol. 1984 Jan;51(1):16-31.

Columnar organization of directionally selective cells in visual area MT of the

Albright TD, Desimone R, Gross CG.
We recorded from single neurons in visual area MT of the macaque in order to
examine the spatial distribution of its directionally selective cells. The
animals were paralyzed and anesthetized with nitrous oxide. All MT neurons (n =
614) responded better to moving stimuli than to stationary stimuli. For 55% of
the neurons, responses to moving stimuli were independent of stimulus color,
shape, length, or orientation. For the remaining cells, stimulus length affected
the response magnitude and tuning bandwidth but not the preferred direction. MT
neurons were divided into four categories on the basis of their sensitivity to
moving stimuli: 60% responded exclusively to one direction of motion, 24%
responded best to one direction with a weaker response in the opposite
direction, 8% responded equally well to two opposite directions of motion, and
8% responded equally well to all directions of motion. The direction preferences
of successively sampled cells on a penetration either changed by small
increments or occasionally by approximately 180 degrees. Thus, there is a
systematic representation of direction of motion. The representation of axis of
motion, i.e., the orientation of the path along which a stimulus moves, is more
continuous than the representation of direction of motion. There was a
systematic relationship between penetration angle and rate of change of
preferred axis of motion, indicating that cells with a similar axis of motion
preference are arranged in vertical columns. Furthermore, axis of motion columns
appear to exist in the form of continuous slabs in area MT. The size of these
slabs is such that 180 degrees of axis of motion are represented in 400-500
micron of cortex. There was also a systematic relationship between penetration
angle and frequency of 180 degrees reversals, indicating that cells with a
similar direction of motion preference are also organized in vertical columns
and cells with opposite direction preferences are located in adjacent columns
within a single axis of motion column. Just as in macaque striate cortex where
approximately 500 micron of cortex contain the mechanism for the local analysis
of stimulus orientation, so in MT approximately 500 micron of cortex contain the
mechanism for the local analysis of stimulus motion.
J Cogn Neurosci. 2004 May;16(4):521-7.

Direct current stimulation over V5 enhances visuomotor coordination by improving
motion perception in humans.

Antal A, Nitsche MA, Kruse W, Kincses TZ, Hoffmann KP, Paulus W.

The primary aim of this study was to determine the extent to which human MT+/V5,
an extrastriate visual area known to mediate motion processing, is involved in
visuomotor coordination. To pursue this we increased or decreased the
excitability of MT+/V5, primary motor, and primary visual cortex by the
application of 7 min of anodal and cathodal transcranial direct current
stimulation (tDCS) in healthy human subjects while they were performing a
visuomotor tracking task involving hand movements. The percentage of correct
tracking movements increased specifically during and immediately after cathodal
stimulation, which decreases cortical excitability, only when V5 was stimulated.
None of the other stimulation conditions affected visuomotor performance. We
propose that the improvement in performance caused by cathodal tDCS of V5 is due
to a focusing effect on to the complex motion perception conditions involved in
this task. This hypothesis was proven by additional experiments: Testing simple
and complex motion perception in dot kinetograms, we found that a diminution in
excitability induced by cathodal stimulation improved the subject's perception
of the direction of the coherent motion only if this was presented among random
dots (complex motion perception), and worsened it if only one motion direction
was presented (simple movement perception). Our data suggest that area V5 is
critically involved in complex motion perception and identification processes
important for visuomotor coordination. The results also raise the possibility of
the usefulness of tDCS in rehabilitation strategies for neurological patients
with visuomotor disorders.
J Neurosci. 2001 Mar 1;21(5):1676-97.

Correlated firing in macaque visual area MT: time scales and relationship to

Bair W, Zohary E, Newsome WT.

Howard Hughes Medical Institute (HHMI), Center for Neural Sc
We studied the simultaneous activity of pairs of neurons recorded with a single
electrode in visual cortical area MT while monkeys performed a direction
discrimination task. Previously, we reported the strength of interneuronal
correlation of spike count on the time scale of the behavioral epoch (2 sec) and
noted its potential impact on signal pooling (Zohary et al., 1994). We have now
examined correlation at longer and shorter time scales and found that pair-wise
cross-correlation was predominantly short term (10-100 msec). Narrow, central
peaks in the spike train cross-correlograms were largely responsible for
correlated spike counts on the time scale of the behavioral epoch. Longer-term
(many seconds to minutes) changes in the responsiveness of single neurons were
observed in auto-correlations; however, these slow changes in time were on
average uncorrelated between neurons. Knowledge of the limited time scale of
correlation allowed the derivation of a more efficient metric for spike count
correlation based on spike timing information, and it also revealed a potential
relative advantage of larger neuronal pools for shorter integration times.
Finally, correlation did not depend on the presence of the visual stimulus or
the behavioral choice of the animal. It varied little with stimulus condition
but was stronger between neurons with similar direction tuning curves. Taken
together, our results strengthen the view that common input, common stimulus
selectivity, and common noise are tightly linked in functioning cortical
J Neurosci. 2004 Aug 18;24(33):7305-23.

Adaptive temporal integration of motion in direction-selective neurons in
macaque visual cortex.

Bair W, Movshon JA.

Center for Neural Science, New York University, New York,
Direction-selective neurons in the primary visual cortex (V1) and the
extrastriate motion area MT/V5 constitute a critical channel that links early
cortical mechanisms of spatiotemporal integration to downstream signals that
underlie motion perception. We studied how temporal integration in
direction-selective cells depends on speed, spatial frequency (SF), and contrast
using randomly moving sinusoidal gratings and spike-triggered average (STA)
analysis. The window of temporal integration revealed by the STAs varied
substantially with stimulus parameters, extending farther back in time for slow
motion, high SF, and low contrast. At low speeds and high SF, STA peaks were
larger, indicating that a single spike often conveyed more information about the
stimulus under conditions in which the mean firing rate was very low. The
observed trends were similar in V1 and MT and offer a physiological correlate
for a large body of psychophysical data on temporal integration. We applied the
same visual stimuli to a model of motion detection based on oriented linear
filters (a motion energy model) that incorporated an integrate-and-fire
mechanism and found that it did not account for the neuronal data. Our results
show that cortical motion processing in V1 and in MT is highly nonlinear and
stimulus dependent. They cast considerable doubt on the ability of simple
oriented filter models to account for the output of direction-selective neurons
in a general manner. Finally, they suggest that spike rate tuning functions may
miss important aspects of the neural coding of motion for stimulus conditions
that evoke low firing rates.
J Neurosci. 2002 Apr 15;22(8):3189-205.

The timing of response onset and offset in macaque visual neurons.

Bair W, Cavanaugh JR, Smith MA, Movshon JA.

Howard Hughes Medical Institute and Center for Neural Science, New Yo
We used fast, pseudorandom temporal sequences of preferred and antipreferred
stimuli to drive neuronal firing rates rapidly between minimal and maximal
across the visual system. Stimuli were tailored to the preferences of cells
recorded in the lateral geniculate nucleus (magnocellular and parvocellular),
primary visual cortex (simple and complex), and the extrastriate motion area MT.
We found that cells took longer to turn on (to increase their firing rate) than
to turn off (to reduce their rate). The latency difference (onset minus offset)
varied from several to tens of milliseconds across cell type and stimulus class
and was correlated with spontaneous or driven firing rates for most cell
classes. The delay for response onset depended on the nature of the stimulus
present before the preferred stimulus appeared, and may result from persistent
inhibition caused by antipreferred stimuli or from suppression that followed the
offset of the preferred stimulus. The onset delay showed three distinct types of
dependence on the temporal sequence of stimuli across classes of cells, implying
that suppression may accumulate or wear off with time. Onset latency is
generally longer, can be more variable, and has marked stimulus dependence
compared with offset latency. This suggests an important role for offset latency
in assessing the speed of information transmission in the visual system and
raises the possibility that signal offsets provide a timing reference for visual
processing. We discuss the origin of the delay in onset latency compared with
offset latency and consider how it may limit the utility of certain feedforward
J Neurophysiol. 1981 Mar;45(3):397-416.

Visual response properties of neurons in four extrastriate visual areas of the
owl monkey (Aotus trivirgatus): a quantitative comparison of medial,
dorsomedial, dorsolateral, and middle tempor
The response properties of 354 single neurons in the medial (M), dorsomedial
(DM), dorsolateral (DL), and middle temporal (MT) visual areas were studied
quantitatively with bar, spot, and random-dot stimuli in chronically implanted
owl monkeys with fixed gaze. 2. A directionality index was computed to compare
the responses to stimuli in the optimal direction with the responses to the
opposing direction of movement. The greater the difference between opposing
directions, the higher the index. MT cells had much higher direction indices to
moving bars than cells in DL, DM, and M. 3. A tuning index was computed for each
cell to compare the responses to bars moving in the optimal direction, or
flashed in the optimal orientation, with the responses in other directions or
orientations within +/- 90 degrees. Cells in all four areas were more sharply
tuned to the orientation of stationary flashed bars than to moving bars,
although a few cells (9/92( were unresponsive in the absence of movement. DM
cells tended to be more sharply tuned to moving bars than cells in the other
areas. 4. Directionality in DM, DL, and MT was relatively unaffected by the use
of single-spot stimuli instead of bars; tuning in all four areas was broader to
spots than bars. 5. Moving arrays of randomly spaced spots were more strongly
excitatory than bar stimuli for many neurons in MT (16/31 cells). These
random-dot stimuli were also effective in M, but evoked no response or weak
responses from most cells in DM and DL. 6. The best velocities of movement were
usually in the range of 10-100 degrees/s, although a few cells (22/227),
primarily in MT (14/69 cells), preferred higher velocities. 7. Receptive fields
of neurons in all four areas were much larger than striate receptive fields.
Eccentricity was positively correlated with receptive-field size (r = 0.62), but
was not correlated with directionality index, tuning index, or best velocity. 8.
The results support the hypothesis that there are specializations of function
among the cortical visual areas.

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