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Dorothe A. Poggel, Dae-Shik Kim, Louis J. Toth; Mapping of posterior parietal areas in fMRI using task relevance and response modalities. Journal of Vision 2006;6(6):537. doi: https://doi.org/10.1167/6.6.537.
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© ARVO (1962-2015); The Authors (2016-present)
Lateral intraparietal area (LIP) is activated in monkeys performing delayed saccade tasks requiring attention to stimulus location or color (Toth & Assad, 2002). A human LIP-analogue was identified with fMRI for delayed saccades to spatial instructions (Sereno et al., 2001). Our goal was to explore whether the same human parietal cortex regions can also be differentially activated by task-instructions and response modality.
We measured BOLD fMRI in 11 subjects (5 male, average age 29 years) with a 3T Philips Intera MR scanner (FEEPI, TR=2500msec, 35 slices, 3mm, TE=35msec, FOV 230x230, 128x128 matrix). Before each block of 16 trials, subjects were instructed to respond to the location (left/right) or color (red/green) of a randomized sequence of cues. Subjects responded by pressing a left or right button. A subset of the sample was re-tested with the same paradigm but responding by delayed saccades. Data were analyzed with BrainVoyager software using GLM and event-related analysis.
Color vs. spatial instructions activated different, neighboring subregions of posterior parietal cortex. For the button-press response, activated areas were located in an area consistent with being homologous to macaque medial intraparietal area (MIP), part of the parietal reach region (PRR). For delayed saccades, separate activation of more lateral parietal areas (homologous to LIP) was observed for color vs. space instructions. Importantly, both areas showed large positional variability between subjects.
Our results suggest that human posterior parietal cortex contains responses modulated by task instruction, with response modality being the prime organizing principle, i.e. a hierarchical architecture of functional maps.
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