scholarly journals Altered sensitivity to motion of area MT neurons following long-term V1 lesions

2017 ◽  
Author(s):  
Maureen A. Hagan ◽  
Tristan A. Chaplin ◽  
Krystel R. Huxlin ◽  
Marcello G. P. Rosa ◽  
Leo L. Lui
Keyword(s):  
Striate Cortex ◽  
Clinical Work ◽  
Neuronal Responses ◽  
Area Mt ◽  
Temporal Area ◽  
Mt Neurons ◽  
Functional Implications ◽  
Thalamic Projections ◽  
Altered Sensitivity

AbstractThe middle temporal area (MT) receives its main afferents from the striate cortex (V1). However, MT also receives direct thalamic projections, which have been hypothesized to play a crucial role in residual vision after V1 lesions. MT neurons continue to respond shortly after V1 lesions, but human clinical work has shown that lesion effects can take up to six months to stabilize, making it important to understand MT responses after long-term deprivation of V1 inputs. We recorded neuronal responses in MT to moving dot stimuli in adult marmoset monkeys, 7-11 months after unilateral V1 lesions. Fewer MT neurons were direction selective, including neurons whose locations corresponded to the intact parts of V1. Firing rates were higher and more variable, and increased with motion strength regardless of direction. These properties could be re-created by a network model with imbalanced inhibition and excitation, providing the first insights into functional implications of long-term plasticity in MT following V1 lesions.

scholarly journals Altered Sensitivity to Motion of Area MT Neurons Following Long-Term V1 Lesions

2019 ◽  
Vol 30 (2) ◽  
pp. 451-464 ◽  
Author(s):  
Maureen A Hagan ◽  
Tristan A Chaplin ◽  
Krystel R Huxlin ◽  
Marcello G P Rosa ◽  
Leo L Lui
Keyword(s):  
Neural Responses ◽  
Neuronal Responses ◽  
Area Mt ◽  
Temporal Area ◽  
Motion Sensitivity ◽  
Firing Rates ◽  
Mt Neurons ◽  
Residual Motion ◽  
Altered Sensitivity

Abstract Primates with primary visual cortex (V1) damage often retain residual motion sensitivity, which is hypothesized to be mediated by middle temporal area (MT). MT neurons continue to respond to stimuli shortly after V1 lesions; however, experimental and clinical studies of lesion-induced plasticity have shown that lesion effects can take several months to stabilize. It is unknown what physiological changes occur in MT and whether neural responses persist long after V1 damage. We recorded neuronal responses in MT to moving dot patterns in adult marmoset monkeys 6–12 months after unilateral V1 lesions. In contrast to results obtained shortly after V1 lesions, we found that fewer MT neurons were direction selective, including neurons expected to still receive projections from remaining parts of V1. The firing rates of most cells increased with increases in motion strength, regardless of stimulus direction. Furthermore, firing rates were higher and more variable than in control MT cells. To test whether these observations could be mechanistically explained by underlying changes in neural circuitry, we created a network model of MT. We found that a local imbalance of inhibition and excitation explained the observed firing rate changes. These results provide the first insights into functional implications of long-term plasticity in MT following V1 lesions.

scholarly journals Feature attention for binocular disparity in primate area MT depends on tuning strength

2015 ◽  
Vol 113 (5) ◽  
pp. 1545-1555 ◽  
Author(s):  
Douglas A. Ruff ◽  
Richard T. Born
Keyword(s):  
Binocular Disparity ◽  
Receptive Fields ◽  
Sensory Information ◽  
Neuronal Population ◽  
Area Mt ◽  
Temporal Area ◽  
Mt Neurons ◽  
Feature Attention ◽  
The Difference ◽  
The Relationship

Attending to a stimulus modulates the responses of sensory neurons that represent features of that stimulus, a phenomenon named “feature attention.” For example, attending to a stimulus containing upward motion enhances the responses of upward-preferring direction-selective neurons in the middle temporal area (MT) and suppresses the responses of downward-preferring neurons, even when the attended stimulus is outside of the spatial receptive fields of the recorded neurons (Treue S, Martinez-Trujillo JC. Nature 399: 575–579, 1999). This modulation renders the representation of sensory information across a neuronal population more selective for the features present in the attended stimulus (Martinez-Trujillo JC, Treue S. Curr Biol 14: 744–751, 2004). We hypothesized that if feature attention modulates neurons according to their tuning preferences, it should also be sensitive to their tuning strength, which is the magnitude of the difference in responses to preferred and null stimuli. We measured how the effects of feature attention on MT neurons in rhesus monkeys ( Macaca mulatta) depended on the relationship between features—in our case, direction of motion and binocular disparity—of the attended stimulus and a neuron's tuning for those features. We found that, as for direction, attention to stimuli containing binocular disparity cues modulated the responses of MT neurons and that the magnitude of the modulation depended on both a neuron's tuning preferences and its tuning strength. Our results suggest that modulation by feature attention may depend not just on which features a neuron represents but also on how well the neuron represents those features.

Motion selectivity in macaque visual cortex. III. Psychophysics and physiology of apparent motion

1986 ◽  
Vol 55 (6) ◽  
pp. 1340-1351 ◽  
Author(s):  
W. T. Newsome ◽  
A. Mikami ◽  
R. H. Wurtz
Keyword(s):  
Apparent Motion ◽  
Cortical Neurons ◽  
Striate Cortex ◽  
Preceding Paper ◽  
Direction Selectivity ◽  
Physiological Data ◽  
Area Mt ◽  
Temporal Area ◽  
Psychophysical Data ◽  
Spatial Interval

We have conducted physiological and psychophysical experiments to identify possible neural substrates of the perception of apparent motion. We used identical sequences of flashed stimuli in both sets of experiments to better compare the responses of cortical neurons and psychophysical observers. Physiological data were obtained from two cortical visual areas, striate cortex (V1) and the middle temporal area (MT). In the previous paper we presented evidence that neuronal thresholds for direction selectivity in extrastriate area MT were similar to psychophysical thresholds for motion perception at the largest effective interflash interval, and thus speed, for a given eccentricity. We now examine physiological and psychophysical thresholds for a broad range of speeds to determine whether such a correspondence exists for speeds below the upper threshold considered in the previous paper. Stimuli were presented in stroboscopic motion of constant apparent speed while the spatial and temporal interflash intervals were systematically varied. For each neuron we measured the largest spatial interval that elicited directionally selective responses at each of several apparent speeds. We calculated the composite performance of neurons in both MT and V1 by averaging the spatial interval necessary for direction selectivity at each apparent speed. We employed the same apparent-motion stimuli for psychophysical experiments with human subjects in which we measured the spatial interval necessary for the perception of motion over a similar range of apparent speeds. We obtained a composite profile of psychophysical performance by averaging thresholds across subjects at each apparent speed. For high apparent speeds, physiological data from MT, but not V1, corresponded closely to the psychophysical data as suggested in the preceding paper. For low apparent speeds, however, physiological data from MT and V1 were similar to each other and to the psychophysical data. It would appear, therefore, that neurons in either V1 or MT could mediate the perceptual effect at low speeds, whereas MT is a stronger candidate for this role at high speeds. We suggest that the neuronal substrate for apparent motion may be distributed over multiple cortical areas, depending upon the speed and spatial interval of the stimulus.

Contrast Dependence of Suppressive Influences in Cortical Area MT of Alert Macaque

2005 ◽  
Vol 93 (3) ◽  
pp. 1809-1815 ◽  
Author(s):  
Christopher C. Pack ◽  
J. Nicholas Hunter ◽  
Richard T. Born
Keyword(s):  
High Contrast ◽  
Area Mt ◽  
Visual Neurons ◽  
Temporal Area ◽  
Low Contrast ◽  
Information Theoretic ◽  
Tuning Curves ◽  
Mt Neurons ◽  
Moving Stimuli ◽  
High Stimulus

Visual neurons are often characterized in terms of their tuning for various stimulus properties, such as shape, color, and velocity. Generally, these tuning curves are further modulated by the overall intensity of the stimulus, such that increasing the contrast increases the firing rate, up to some maximum. In this paper, we describe the tuning of neurons in the middle temporal area (MT or V5) of macaque visual cortex for moving stimuli of varying contrast. We find that, for some MT neurons, tuning curves for stimulus direction, speed, and size are shaped in part by suppressive influences that are present at high stimulus contrast but weak or nonexistent at low contrast. For most neurons, the suppression is direction-specific and strongest for large, slow-moving stimuli. The surprising consequence of this phenomenon is that some MT neurons actually fire more vigorously to a large low-contrast stimulus than to one of high contrast. These results are consistent with recent perceptual observations, as well as with information-theoretic models, which hypothesize that the visual system seeks to reduce redundancy at high contrast while maintaining sensitivity at low contrast.

Microstimulation of Cortical Area MT Affects Performance on a Visual Working Memory Task

2001 ◽  
Vol 85 (1) ◽  
pp. 187-196 ◽  
Author(s):  
James W. Bisley ◽  
Daniel Zaksas ◽  
Tatiana Pasternak
Keyword(s):  
Working Memory ◽  
Visual Motion ◽  
Memory Task ◽  
Stimulus Motion ◽  
Area Mt ◽  
Directional Information ◽  
Temporal Area ◽  
Mt Neurons ◽  
Directional Motion ◽  
Term Storage

We applied electrical stimulation to physiologically identified sites in macaque middle temporal area (MT) to examine its role in short-term storage of recently encoded information about stimulus motion. We used a behavioral task in which monkeys compared the directions of two moving random-dot stimuli, sample and test, separated by a 1.5-s delay. Four sample directions were used for each site, and the animals had to indicate whether the direction of motion in the sample was the same as or different to the direction of motion in the test. We found that the effect of stimulation of the same directional column in MT depended on the behavioral state of the animal. Although stimulation had strong effects when applied during the encoding and the storage components of the task, these effects were not equivalent. Stimulation applied during the presentation of the sample produced signals interpreted by the monkeys as directional motion. However, the same stimulation introduced during the period of storage no longer produced signals interpreted as unambiguous directional information. We conclude that the directional information used by the monkeys in the working memory task is likely to be provided by neurons in MT, and the use of this information appears to be dependent on the portion of the task during which stimulation was delivered. Finally, the disruptive effects of stimulation during the delay suggest that MT neurons not only participate in the encoding of visual motion information but also in its storage by either maintaining an active connection with the circuitry involved in storage or being an integral component of that circuitry.

scholarly journals Population Anisotropy in Area MT Explains a Perceptual Difference Between Near and Far Disparity Motion Segmentation

2011 ◽  
Vol 105 (1) ◽  
pp. 200-208 ◽  
Author(s):  
Finnegan J. Calabro ◽  
Lucia M. Vaina
Keyword(s):  
Visual Cues ◽  
Visual Motion ◽  
Population Distribution ◽  
Normal Population ◽  
Motion Processing ◽  
Area Mt ◽  
Temporal Area ◽  
Motion Discrimination ◽  
Mt Neurons ◽  
Simulated Performance

Segmentation of the visual scene into relevant object components is a fundamental process for successfully interacting with our surroundings. Many visual cues, including motion and binocular disparity, support segmentation, yet the mechanisms using these cues are unclear. We used a psychophysical motion discrimination task in which noise dots were displaced in depth to investigate the role of segmentation through disparity cues in visual motion stimuli ( experiment 1). We found a subtle, but significant, bias indicating that near disparity noise disrupted the segmentation of motion more than equidistant far disparity noise. A control experiment showed that the near-far difference could not be attributed to attention ( experiment 2). To account for the near-far bias, we constructed a biologically constrained model using recordings from neurons in the middle temporal area (MT) to simulate human observers' performance on experiment 1. Performance of the model of MT neurons showed a near-disparity skew similar to that shown by human observers. To isolate the cause of the skew, we simulated performance of a model containing units derived from properties of MT neurons, using phase-modulated Gabor disparity tuning. Using a skewed-normal population distribution of preferred disparities, the model reproduced the elevated motion discrimination thresholds for near-disparity noise, whereas a skewed-normal population of phases (creating individually asymmetric units) did not lead to any performance skew. Results from the model suggest that the properties of neurons in area MT are computationally sufficient to perform disparity segmentation during motion processing and produce similar disparity biases as those produced by human observers.

scholarly journals Misperceptions of speed are accounted for by the responses of neurons in macaque cortical area MT

2011 ◽  
Vol 105 (3) ◽  
pp. 1199-1211 ◽  
Author(s):  
Pınar Boyraz ◽  
Stefan Treue
Keyword(s):  
Human Subjects ◽  
General Mechanism ◽  
Physiological Data ◽  
Neural Basis ◽  
Area Mt ◽  
Temporal Area ◽  
Tuning Curves ◽  
Mt Neurons ◽  
Random Dot Patterns ◽  
Perceived Speed

In humans, the perceived speed of random dot patterns (RDP) moving within small apertures is faster than that of RDPs moving within larger apertures at the same physical speed. To investigate the neural basis of this illusion, we recorded the responses of direction- and speed-selective neurons in the middle temporal area (MT) of macaque monkeys to stimuli varying in size and speed. Our results show that the preferred speed of MT neurons is slower for smaller stimuli. This effect was larger for neurons preferring faster speeds, matching our psychophysical observation in human subjects that the magnitude of the misperception is larger at higher stimulus speeds. Our physiological data indicate that, across a population of speed-tuned neurons in MT, decreasing the size of a stimulus would shift the activity profile to neurons tuned for higher speeds. Modeling a labeled-line readout of this shifted profile, we show an increased apparent speed, in line with the psychophysical observations. This link strengthens the evidence for a causal role of area MT in speed perception. The systematic shift in tuning curves of single neurons with stimulus size might reflect a general mechanism for feature-mismatch illusions in visual perception.

Spatial Summation, End Inhibition and Side Inhibition in the Middle Temporal Visual Area (MT)

2007 ◽  
Vol 97 (2) ◽  
pp. 1135-1148 ◽  
Author(s):  
Leo L. Lui ◽  
James A. Bourne ◽  
Marcello G. P. Rosa
Keyword(s):  
Spatial Summation ◽  
Distinct Group ◽  
Sine Wave ◽  
Wide Field ◽  
Area Mt ◽  
Temporal Area ◽  
Middle Temporal ◽  
Mt Neurons ◽  
Layer 4 ◽  
Stimulus Length

We investigated the responses of single neurons in the middle temporal area (MT) of anesthetized marmoset monkeys to sine-wave gratings of various lengths and widths. For the vast majority of MT cells maximal responses were obtained on presentation of gratings of specific dimensions, which were typically asymmetrical along the length and width axes. The strength of end inhibition was dependent on the width of the stimulus, with many cells showing clear end inhibition only when wide gratings were used. Conversely, the strength of side inhibition was dependent on stimulus length. Furthermore, for over one third of MT cells length summation properties could not be defined without consideration of stimulus width and vice versa. These neurons, which we refer to as “length–width inseparable” (LWI) cells, were rare in layer 4. The majority of LWI neurons was strongly inhibited by wide-field stimuli and responded preferentially to gratings that were elongated, along either the length or width dimensions. However, rather than forming a homogeneous and entirely distinct group, LWI cells represented the upper end of a continuum of complexity in spatial summation response properties, which characterized the population of MT cells. Only a minority of MT neurons (22.3%) showed no evidence of inhibition by wide-field stimuli, with this type of response being common among layer 5 cells. These results demonstrate distinct patterns of spatial selectivity in MT, supporting the notion that neurons in this area can perform various roles in terms of grouping and segmentation of motion signals.

Intraindividual Variability and Stability of Affect and Well-Being

GeroPsych ◽  
2013 ◽  
Vol 26 (3) ◽  
pp. 185-199 ◽  
Author(s):  
Christina Röcke ◽  
Annette Brose
Keyword(s):  
Age Differences ◽  
Well Being ◽  
Subjective Well Being ◽  
Emotional Experiences ◽  
Short Term ◽  
Regulatory Processes ◽  
Functional Implications ◽  
Methodological Approaches ◽  
Underlying Processes

Whereas subjective well-being remains relatively stable across adulthood, emotional experiences show remarkable short-term variability, with younger and older adults differing in both amount and correlates. Repeatedly assessed affect data captures both the dynamics and stability as well as stabilization that may indicate emotion-regulatory processes. The article reviews (1) research approaches to intraindividual affect variability, (2) functional implications of affect variability, and (3) age differences in affect variability. Based on this review, we discuss how the broader literature on emotional aging can be better integrated with theories and concepts of intraindividual affect variability by using appropriate methodological approaches. Finally, we show how a better understanding of affect variability and its underlying processes could contribute to the long-term stabilization of well-being in old age.

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