Biology subjects

Patel, G. H.

Publications and source records attributed to Patel, G. H..

3 recordsLinked to original sources

bioRxiv2018

Comparison of stimulus-evoked BOLD responses in human and monkey visual cortex

We characterized the blood oxygenation level dependent (BOLD) signal in humans and macaque monkeys by comparing the response in visual cortex to a single checkerboard or two checkerboards, spaced 1.5, 3.0, or 4.5 s apart. We found that the magnitude and shape of the BOLD response to a single checkerboard was similar in the two species. In addition, we found that the BOLD responses summed similarly, and that at an inter-stimulus interval (ISI) of 4.5 sec BOLD summation was nearly linear in both species. When comparing the ratio of the amplitude of the response to the second checkerboard at the 4.5 sec ISI with that of the single checkerboard between subjects in both species, the results from both monkey subjects fell within one standard deviation of the mean human results (human mean (n=12): .95 +/- .31 second/single response amplitude; monkey 1: 1.16; monkey 2: .86). At the shorter ISIs, both species demonstrated increased suppression of the BOLD response to the second checkerboard. These findings indicate that the magnitude of the BOLD response to events separated by 4.5 seconds can be accurately measured in and compared between human and monkey visual cortex.

neuroscience↗

bioRxiv2018

Topographic Organization of Extraoccipital Visual Processing Areas in the Macaque

The macaque visual system has long been used as a model for investigating the processing of incoming visual stimuli results from the coordinated work of a distributed network of areas interacting at many different levels (Felleman and Van Essen, 1991). While much is known about the organization and layout of the occipital visual areas, there are still substantial gaps in our understanding of layout and organization of the higher-level areas. The goal of this study is to describe the whole brain functional anatomy using BOLD-fMRI in macaques performing a series of demanding visuospatial attention tasks. We wish to study the spatial specificity of visual responses in terms of contralateral preference, i.e. stronger responses to contralateral visual stimuli, as well as retinotopic organization both in terms of polar angle and eccentricity. We found that most visuospatial processing areas only respond to contralaterally presented stimuli; ipsilaterally presented stimuli evoked little or no activity in these areas. Additionally, we found that LIP, MT, and possibly PITd contained polar-angle maps of the contralateral hemifield. These same areas, plus FEF and area 46, appear to have separate representations of the fovea and periphery. When compared to previous human fMRI studies, these results indicate that there may be significant differences between macaque visual processing areas and their putative human homologues.

neuroscience↗

bioRxiv2018

Attentional Modulation of Macaque Visual Processing Areas

Introduction Introduction Materials and Methods Results Discussion References The visual expectation that an object will appear at a certain location or time may increase the accuracy and speed of its detection (Eriksen and Hoffman, 1974; Posner, 1980; Carrasco et al., 2000; Dosher and Z-L., 2000). The ability to use prior information to enhance the processing of visual stimuli at a specific location is critical for quickly sorting through the myriad of incoming stimuli and making decisions regarding future actions. This selection process, known as visual attention, appears to be fundamental to our ability to navigate and interact with the environment, and accordingly has been the focus of innumerable psychological and neurobiological studies (Pa ...

neuroscience↗