Browsing by Author "Mayo, J Patrick"

Now showing 1 - 8 of 8
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    A Probabilistic Approach to Receptive Field Mapping in the Frontal Eye Fields.
    (Frontiers in systems neuroscience, 2016-01) Mayo, J Patrick; Morrison, Robert M; Smith, Matthew A
    Studies of the neuronal mechanisms of perisaccadic vision often lack the resolution needed to determine important changes in receptive field (RF) structure. Such limited analytical power can lead to inaccurate descriptions of visuomotor processing. To address this issue, we developed a precise, probabilistic technique that uses a generalized linear model (GLM) for mapping the visual RFs of frontal eye field (FEF) neurons during stable fixation (Mayo et al., 2015). We previously found that full-field RF maps could be obtained using 1-8 dot stimuli presented at frame rates of 10-150 ms. FEF responses were generally robust to changes in the number of stimuli presented or the rate of presentation, which allowed us to visualize RFs over a range of spatial and temporal resolutions. Here, we compare the quality of RFs obtained over different stimulus and GLM parameters to facilitate future work on the detailed mapping of FEF RFs. We first evaluate the interactions between the number of stimuli presented per trial, the total number of trials, and the quality of RF mapping. Next, we vary the spatial resolution of our approach to illustrate the tradeoff between visualizing RF sub-structure and sampling at high resolutions. We then evaluate local smoothing as a possible correction for situations where under-sampling occurs. Finally, we provide a preliminary demonstration of the usefulness of a probabilistic approach for visualizing full-field perisaccadic RF shifts. Our results present a powerful, and perhaps necessary, framework for studying perisaccadic vision that is applicable to FEF and possibly other visuomotor regions of the brain.
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    A Refined Neuronal Population Measure of Visual Attention.
    (PloS one, 2015-01) Mayo, J Patrick; Cohen, Marlene R; Maunsell, John HR
    Neurophysiological studies of cognitive mechanisms such as visual attention typically ignore trial-by-trial variability and instead report mean differences averaged across many trials. Advances in electrophysiology allow for the simultaneous recording of small populations of neurons, which may obviate the need for averaging activity over trials. We recently introduced a method called the attention axis that uses multi-electrode recordings to provide estimates of attentional state of behaving monkeys on individual trials. Here, we refine this method to eliminate problems that can cause bias in estimates of attentional state in certain scenarios. We demonstrate the sources of these problems using simulations and propose an amendment to the previous formulation that provides superior performance in trial-by-trial assessments of attentional state.
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    Dynamics of visual receptive fields in the macaque frontal eye field.
    (J Neurophysiol, 2015-12) Mayo, J Patrick; DiTomasso, Amie R; Sommer, Marc A; Smith, Matthew A
    Neuronal receptive fields (RFs) provide the foundation for understanding systems-level sensory processing. In early visual areas, investigators have mapped RFs in detail using stochastic stimuli and sophisticated analytical approaches. Much less is known about RFs in prefrontal cortex. Visual stimuli used for mapping RFs in prefrontal cortex tend to cover a small range of spatial and temporal parameters, making it difficult to understand their role in visual processing. To address these shortcomings, we implemented a generalized linear model to measure the RFs of neurons in the macaque frontal eye field (FEF) in response to sparse, full-field stimuli. Our high-resolution, probabilistic approach tracked the evolution of RFs during passive fixation, and we validated our results against conventional measures. We found that FEF neurons exhibited a surprising level of sensitivity to stimuli presented as briefly as 10 ms or to multiple dots presented simultaneously, suggesting that FEF visual responses are more precise than previously appreciated. FEF RF spatial structures were largely maintained over time and between stimulus conditions. Our results demonstrate that the application of probabilistic RF mapping to FEF and similar association areas is an important tool for clarifying the neuronal mechanisms of cognition.
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    Feature-specific clusters of neurons and decision-related neuronal activity.
    (The Journal of neuroscience : the official journal of the Society for Neuroscience, 2014-06) Mayo, J Patrick; Verhoef, Bram-Ernst
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    Graded Neuronal Modulations Related to Visual Spatial Attention.
    (The Journal of neuroscience : the official journal of the Society for Neuroscience, 2016-05) Mayo, J Patrick; Maunsell, John HR
    UNLABELLED:Studies of visual attention in monkeys typically measure neuronal activity when the stimulus event to be detected occurs at a cued location versus when it occurs at an uncued location. But this approach does not address how neuronal activity changes relative to conditions where attention is unconstrained by cueing. Human psychophysical studies have used neutral cueing conditions and found that neutrally cued behavioral performance is generally intermediate to that of cued and uncued conditions (Posner et al., 1978; Mangun and Hillyard, 1990; Montagna et al., 2009). To determine whether the neuronal correlates of visual attention during neutral cueing are similarly intermediate, we trained macaque monkeys to detect changes in stimulus orientation that were more likely to occur at one location (cued) than another (uncued), or were equally likely to occur at either stimulus location (neutral). Consistent with human studies, performance was best when the location was cued, intermediate when both locations were neutrally cued, and worst when the location was uncued. Neuronal modulations in visual area V4 were also graded as a function of cue validity and behavioral performance. By recording from both hemispheres simultaneously, we investigated the possibility of switching attention between stimulus locations during neutral cueing. The results failed to support a unitary "spotlight" of attention. Overall, our findings indicate that attention-related changes in V4 are graded to accommodate task demands. SIGNIFICANCE STATEMENT:Studies of the neuronal correlates of attention in monkeys typically use visual cues to manipulate where attention is focused ("cued" vs "uncued"). Human psychophysical studies often also include neutrally cued trials to study how attention naturally varies between points of interest. But the neuronal correlates of this neutral condition are unclear. We measured behavioral performance and neuronal activity in cued, uncued, and neutrally cued blocks of trials. Behavioral performance and neuronal responses during neutral cueing were intermediate to those of the cued and uncued conditions. We found no signatures of a single mechanism of attention that switches between stimulus locations. Thus, attention-related changes in neuronal activity are largely hemisphere-specific and graded according to task demands.
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    Neuronal adaptation caused by sequential visual stimulation in the frontal eye field.
    (J Neurophysiol, 2008-10) Mayo, J Patrick; Sommer, Marc A
    Images on the retina can change drastically in only a few milliseconds. A robust description of visual temporal processing is therefore necessary to understand visual analysis in the real world. To this end, we studied subsecond visual changes and asked how prefrontal neurons in monkeys respond to stimuli presented in quick succession. We recorded the visual responses of single neurons in the frontal eye field (FEF), a prefrontal area polysynaptically removed from the retina that is involved with higher level cognition. For comparison, we also recorded from small groups of neurons in the superficial superior colliculus (supSC), an area that receives direct retinal input. Two sequential flashes of light at varying interstimulus intervals were presented in a neuron's receptive field. We found pervasive neuronal adaptation in FEF and supSC. Visual responses to the second stimulus were diminished for up to half a second after the first stimulus presentation. Adaptation required a similar amount of time to return to full responsiveness in both structures, but there was significantly more neuronal adaptation overall in FEF. Adaptation was not affected by saccades, although visual responses to single stimuli were transiently suppressed postsaccadically. Our FEF and supSC results systematically document subsecond visual adaptation in prefrontal cortex and show that this adaptation is comparable to, but stronger than, adaptation found earlier in the visual system.
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    Neuronal Adaptation: Tired Neurons or Wired Networks?
    (Trends in neurosciences, 2017-03) Mayo, J Patrick; Smith, Matthew A
    Neuronal adaptation - time-dependent modulation of sensory responses following sequential stimuli - is thought to be a consequence of synaptic plasticity. But recent, empirically-grounded, modeling by Quiroga and colleagues demonstrates that the adaptation of visual cortical responses can be described by recurrent network connections with fixed synaptic weights.
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    Neuronal correlates of visual time perception at brief timescales.
    (Proc Natl Acad Sci U S A, 2013-01-22) Mayo, J Patrick; Sommer, Marc A
    Successful interaction with the world depends on accurate perception of the timing of external events. Neurons at early stages of the primate visual system represent time-varying stimuli with high precision. However, it is unknown whether this temporal fidelity is maintained in the prefrontal cortex, where changes in neuronal activity generally correlate with changes in perception. One reason to suspect that it is not maintained is that humans experience surprisingly large fluctuations in the perception of time. To investigate the neuronal correlates of time perception, we recorded from neurons in the prefrontal cortex and midbrain of monkeys performing a temporal-discrimination task. Visual time intervals were presented at a timescale relevant to natural behavior (<500 ms). At this brief timescale, neuronal adaptation--time-dependent changes in the size of successive responses--occurs. We found that visual activity fluctuated with timing judgments in the prefrontal cortex but not in comparable midbrain areas. Surprisingly, only response strength, not timing, predicted task performance. Intervals perceived as longer were associated with larger visual responses and shorter intervals with smaller responses, matching the dynamics of adaptation. These results suggest that the magnitude of prefrontal activity may be read out to provide temporal information that contributes to judging the passage of time.