Biomedical subjects

Heather L Dean

Publications and source records attributed to Heather L Dean.

4 recordsLinked to original sources

PubMed2006

Allocentric spatial referencing of neuronal activity in macaque posterior cingulate cortex.

Neuronal activity in posterior cingulate cortex (CGp) is modulated by visual stimulation, saccades, and eye position, suggesting a role for this area in visuospatial transformations. The goal of this study was to determine whether neuronal responses in CGp are anchored to the eyes, head, or outside the body (allocentrically). To discriminate retinocentric from nonretinocentric spatial referencing, the activity of single CGp neurons was recorded while monkeys (Macaca mulatta) performed delayed-saccade trials initiated randomly from three different starting positions to a linear array of targets passing through the neuronal response field. For most neurons, tuning curves, segregated by fixation point, aligned more closely when plotted with respect to the display than when plotted with respect to the eye, suggesting a nonretinocentric frame of reference. A second experiment differentiated between spatial referencing in coordinates anchored to the head or body and allocentric spatial referencing. Monkeys shifted gaze from a central fixation point to the array of previously used targets both before and after whole-body rotation with respect to the display. For most neurons, tuning curves, segregated by fixation position, aligned more closely when plotted as a function of target position in the room than when plotted as a function of target position with respect to the monkey. These data indicate that a population of CGp neurons encodes visuospatial events in allocentric coordinates.

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PubMed2004

Visual and saccade-related activity in macaque posterior cingulate cortex.

Previous neurophysiological studies have reported that neurons in posterior cingulate cortex (PCC) respond after eye movements, and that these responses may vary with ambient illumination. In monkeys, PCC neurons also respond after the illumination of large visual patterns but not after the illumination of small visual targets on either reflexive saccade tasks or peripheral attention tasks. These observations suggest that neuronal activity in PCC is modulated by behavioral context, which varies with the timing and spatial distribution of visual and oculomotor events. To test this hypothesis, we measured the spatial and temporal response properties of single PCC neurons in monkeys performing saccades in which target location and movement timing varied unpredictably. Specifically, an unsignaled delay between target onset and movement onset permitted us to temporally dissociate changes in PCC activity associated with either event. Response fields constructed from these data demonstrated that many PCC neurons were activated after the illumination of small contralateral visual targets, as well as after the onset of contraversive saccades guided by those targets. In addition, the PCC population maintained selectivity for small contralateral targets during delays of up to 600 ms. Overall, PCC activation was highly variable trial to trial and selective for a broad range of directions and amplitudes. Planar functions described response fields nearly as well as broadly tuned 2-dimensional Gaussian functions. Additionally, the overall responsiveness of PCC neurons decreased during delays when both a fixation stimulus and a saccade target were visible, suggesting a modulation by divided attention. Finally, the strength of the neuronal response after target onset was correlated with saccade accuracy on delayed-saccade trials. Thus PCC neurons may signal salient visual and oculomotor events, consistent with a role in visual orienting and attention.

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PubMed2004

Emotion-attention network interactions during a visual oddball task.

Emotional and attentional functions are known to be distributed along ventral and dorsal networks in the brain, respectively. However, the interactions between these systems remain to be specified. The present study used event-related functional magnetic resonance imaging (fMRI) to investigate how attentional focus can modulate the neural activity elicited by scenes that vary in emotional content. In a visual oddball task, aversive and neutral scenes were presented intermittently among circles and squares. The squares were frequent standard events, whereas the other novel stimulus categories occurred rarely. One experimental group [N=10] was instructed to count the circles, whereas another group [N=12] counted the emotional scenes. A main effect of emotion was found in the amygdala (AMG) and ventral frontotemporal cortices. In these regions, activation was significantly greater for emotional than neutral stimuli but was invariant to attentional focus. A main effect of attentional focus was found in dorsal frontoparietal cortices, whose activity signaled task-relevant target events irrespective of emotional content. The only brain region that was sensitive to both emotion and attentional focus was the anterior cingulate gyrus (ACG). When circles were task-relevant, the ACG responded equally to circle targets and distracting emotional scenes. The ACG response to emotional scenes increased when they were task-relevant, and the response to circles concomitantly decreased. These findings support and extend prominent network theories of emotion-attention interactions that highlight the integrative role played by the anterior cingulate.

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PubMed2003

Saccade reward signals in posterior cingulate cortex.

Movement selection depends on the outcome of prior behavior. Posterior cingulate cortex (CGp) is strongly connected with both limbic and oculomotor circuitry, and CGp neurons respond following saccades, suggesting a role in signaling the motivational outcome of gaze shifts. To test this hypothesis, single CGp neurons were studied in monkeys while they shifted gaze to visual targets for liquid rewards that varied in size or were delivered probabilistically. CGp neurons responded following saccades as well as following reward delivery, and these responses were correlated with reward size. CGp neurons also responded following the omission of predicted rewards. The timing of CGp activation and its modulation by reward could provide signals useful for updating representations of expected saccade value.

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