Biomedical subjects

Aaron P Tansy

Publications and source records attributed to Aaron P Tansy.

5 recordsLinked to original sources

PubMed2005

A functional MRI study of preparatory signals for spatial location and objects.

We investigated preparatory signals for spatial location and objects in normal observers using functional magnetic resonance imaging (fMRI). Activity for attention-directing cues was separated from activity for subsequent test arrays containing the target stimulus. Subjects were more accurate in discriminating a target face among distracters when they knew in advance its location (spatial directional cue), as compared to when the target could randomly appear at one of two locations (spatial neutral cue), indicating that the spatial cue was used. Spatially specific activations occurred in a region at the intersection of the ventral intraparietal sulcus and transverse occipital sulcus (vIPS-TOS), which showed significantly stronger activation for rightward- than leftward-directing cues, while other fronto-parietal areas were activated by the cue but did not show spatial specificity. In visual cortex, activity was weak or absent in retinotopic occipital regions following attention-directing cues and this activity was not spatially specific. In a separate task, subject discriminated a target outdoor scene among distracters after the presentation of spatial neutral cues. There was no significant difference in dorsal frontoparietal activity during the face versus scene discrimination task. Also, there was only weak evidence for selective preparatory activity in ventral object-selective regions, although the activation of these regions to the subsequent test array did depend upon which discrimination (face or place) was performed. We conclude first that under certain circumstances, spatial cues that produce strong behavioral effects may modulate parietal-occipital regions in a spatially specific manner without producing similar modulations in retinotopic occipital regions. Second, attentional modulations of object-selective regions in temporal-occipital cortex can occur even though preparatory object-selective modulations of those regions are absent or weak.

Analysis of Variance↗

PubMed2003

Quantitative analysis of attention and detection signals during visual search.

Prior work has distinguished regions in the intraparietal sulcus (IPs) and frontal eye field (FEF) involved in the voluntary control of attention, from more ventral regions in the temporoparietal junction (TPJ) involved in target detection. The present results show that when subjects search for and detect a visual target stimulus among nontargets, these regions show sensory-, search-, and detection-related signals that both confirm and refine these functional distinctions. The different signals were isolated by an additive model that accounted for a large fraction of BOLD (blood oxygenation level-dependent) signal modulation over the brain. Both IPs and FEF were activated during search through nontargets, consistent with a role in maintaining attention-related signals during search. However, unlike FEF, IPs also showed stimulus-related activations, and may combine signals related to sensory and task-dependent components of salience. Although IPs-FEF showed search-related activations, the TPJ was deactivated during search. TPJ activations were confined to detection-related signals. These results provide a much stronger dissociation between the TPJ and IPs-FEF than previous work, while indicating functional differences between frontal and parietal regions that are often coactivated in studies of attention. Finally, continuous flow models of information processing predict that during search, signals from missed targets should be fed from sensory to associative regions rather than being gated by the decision criterion. Correspondingly, missed targets significantly activated parietal (e.g., right TPJ) and frontal (e.g., anterior insula, anterior cingulate) regions, although with a smaller magnitude than detected targets. Surprisingly, many cortical regions showed equivalent signals from detected targets and the completion of target-absent trials, reflecting a widespread signal unrelated to motor execution.

Attention↗

PubMed2002

Word retrieval learning modulates right frontal cortex in patients with left frontal damage.

Previous studies have suggested that recovery or compensation of language function after a lesion in the left hemisphere may depend on mechanisms in the right hemisphere. However, a direct relationship between performance and right hemisphere activity has not been established. Here, we show that patients with left frontal lesions and partially recovered aphasia learn, at a normal rate, a novel word retrieval task that requires the damaged cortex. Verbal learning is accompanied by specific response decrements in right frontal and right occipital cortex, strongly supporting the compensatory role of the right hemisphere. Furthermore, responses in left occipital cortex are abnormal and not modulated by practice. These findings indicate that frontal cortex is a source of top-down signals during learning.

Aphasia, Broca↗

PubMed2002

Two attentional processes in the parietal lobe.

We report fMRI evidence for two attentional processes in parietal cortex. Subjects matched a feature, cued by a word, to a test display of moving colored dots. Either color (red, green) or motion direction (left, right) was cued on mixed scans while only one dimension was cued on blocked scans. An event-related paradigm separated the preparatory activity generated by the cue from the subsequent activity related to the test display. One attentional process specified task information while a second process was motion selective. During the cue period, a pure effect of task specification was observed in left frontal cortex while combined effects of task specification and motion selectivity were observed in left posterior parietal cortex. The frontal task-specification signal may have been the source of the corresponding signal in parietal cortex. Effects of task specification generalized over cue dimension, indicating that the information was coded in a sufficiently abstract form to affect color and motion processing. During the subsequent test period, task-specification and motion-selective signals were again observed in left parietal cortex. Task specification did not significantly affect occipital motion-selective regions, such as MT+, however, indicating that this process did not influence the lower cortical tier of the motion processing stream. These results provide evidence for general and specialized task representations within left parietal cortex during task preparation and execution.

Analysis of Variance↗

PubMed2002

Reactivation of networks involved in preparatory states.

We report an endogenous signal that has a widespread cortical distribution and is time-locked to the termination of a sustained state of task-readiness. In three event-related functional magnetic resonance imaging (fMRI) experiments, subjects saw an arrow cue that predicted either the direction of motion or the location of a subsequent test stimulus. A reactivation of the BOLD (blood oxygenation level-dependent) signal occurred at the termination of the state of readiness in occipital regions that were transiently activated by the cue and in frontal-parietal regions that maintained an attentional set over the trial. Moreover, a delayed activation occurred in prefrontal and temporo-parietal regions that did not initially respond to the cue and that have been implicated in re-orienting attention to novel sensory events. These latter regions may have generated control signals that ended the state of readiness in regions active during the cue period. These results indicate that terminating a state of readiness produces a widely distributed cortical signal and suggest that areas involved in a preparatory state may be maintained as a network which can be modulated as a whole.

Attention↗