Biomedical subjects

Simon J Graham

Publications and source records attributed to Simon J Graham.

23 records · Page 2Linked to original sources

PubMed2003

A platform for combining virtual reality experiments with functional magnetic resonance imaging.

How the brain functions during behavioural tasks conducted in virtual reality (VR) remains largely unresolved. This issue is extremely important both in terms of establishing the benefits of VR through basic science, as well as for future optimization of tasks conducted in VR environments. Here, the authors describe their current work to develop a testing platform for conducting VR experiments that can be probed by functional magnetic resonance imaging (fMRI) to measure brain activity. Examples involving human spatial navigation and data glove operation illustrate the technical feasibility of the approach and introduce thought-provoking observations of brain activation patterns. Future research directions for combined use of VR and fMRI are also discussed.

Brain↗

PubMed2003

A data glove with tactile feedback for FMRI of virtual reality experiments.

Virtual reality (VR) technology is increasingly recognized as a useful tool for the assessment and rehabilitation of neurologic and psychiatric disorders. The hope that VR can accurately mimic real-life events is also of great interest in basic neuroscience, to identify the brain activity that underlies complex behavior by combining VR with techniques such as functional magnetic resonance imaging (fMRI). Toward these applications, in this study we designed and validated an fMRI-compatible data glove with a built-in vibratory stimulus device for tactile feedback during VR experiments. A simple VR-fMRI experiment was performed at 3.0 Tesla on four young healthy adults involving touching a virtual object with and without tactile feedback. The usefulness of the data glove was subsequently assessed using a series of questionnaires, behavioral performance, and the resulting activation images. Questionnaire scores indicated positive opinions with respect to the data glove, the tactile feedback, and the experimental paradigm. All subjects felt comfortable in the scanner during the VR experiment and were able to perform all aspects of the tasks successfully and with reasonable accuracy. In addition, activation maps showed the anticipated modulations in motor, somatosensory, and parietal cortex. These results support that tactile feedback enhances the realism of virtual hand-object interactions, and that the tactile data glove is suitable for use in other VR-fMRI research applications (e.g., VR physical therapy for stroke recovery).

Adult↗

PubMed2003

In search of the emotional self: an fMRI study using positive and negative emotional words.

OBJECTIVE: The authors used functional magnetic resonance imaging (fMRI) to define the neural regions mediating self-referential processing of emotional stimuli and to explore how these regions are influenced by the emotional valence of the stimulus. METHOD: Ten healthy subjects were presented with words describing positive and negative personality traits during fMRI scanning in three different conditions. In the self-referential processing condition, subjects judged whether they thought each trait described them. In the other-referential processing condition, subjects judged whether the stimulus described a generally desirable trait. In the letter-recognition control condition, subjects indicated whether the word contained a specific target letter. RESULTS: The self-referential condition induced bilateral activation in the dorsomedial prefrontal cortex, whereas the other-referential condition induced activation in lateral prefrontal areas. Activation in the right dorsomedial prefrontal cortex was unique to the self-referential condition regardless of the valence of the words, although positive words produced a more robust activation than did negative words. In the self-referential condition, differences between the processing of positive and negative words were seen in regions outside the medial frontal cortex, with reductions in the insula, temporal and occipital regions, and inferior parietal regions associated with negative words. CONCLUSIONS: A widely distributed network of brain areas contributes to emotional processing. Among these regions, the right dorsomedial prefrontal cortex is one main area mediating self-reference. By providing a personal perspective in the evaluation of emotional stimuli, the right dorsomedial prefrontal cortex may mediate cognitive processes, such as those involved in psychotherapy, that guide self-regulation of emotional experience.

Adult↗

PubMed2002

Task-relevant modulation of contralateral and ipsilateral primary somatosensory cortex and the role of a prefrontal-cortical sensory gating system.

Electrophysiological studies have shown that task-relevant somatosensory information leads to selective facilitation within the primary somatosensory cortex (SI). The purpose of the present study was (1) to further explore the relationship between the relevancy of stimuli and activation within the contralateral and ipsilateral SI and (2) to provide further insight into the specific sensory gating network responsible for modulating neural activity within SI. Functional MRI of 12 normal subjects was performed with vibrotactile stimuli presented to the pad of the index finger. In experiment 1, the stimulus was presented to either the left or the right hand. Subjects were required to detect transient changes in stimulus frequency. In experiment 2, stimuli were presented to either the right hand alone or both hands simultaneously. Stimuli were applied either (A) passively or (B) when subjects were asked to detect frequency changes that occurred to the right hand only. In experiment 1, task-relevant somatosensory stimulation led not only to enhanced contralateral SI activity, but also to a suppression of activity in the ipsilateral SI. In experiment 2, SI activation was enhanced when stimuli were task-relevant, compared to that observed with passive input. When stimuli were presented simultaneously to both hands, only those that were task-relevant increased SI activation. This was associated with recruitment of a network of cortical regions, including the right prefrontal cortex (Brodmann area 9). We conclude that SI modulation is dependent on task relevancy and that this modulation may be regulated, at least in part, by the prefrontal cortex.

Adult↗

PubMed2002

Somatosensory gating and recovery from stroke involving the thalamus.

BACKGROUND AND PURPOSE: In the undamaged brain, sensory input to the cortex is intricately controlled via sensory gating mechanisms. Given the role of corticothalamic pathways in this control, it was hypothesized that in patients recovering from thalamic stroke there would be evidence of disrupted sensory gating and that efficient control of cortical sensory inputs would emerge during recovery. METHODS: Four patients were tested serially after stroke from 1 to 24 weeks after injury. Perceptual thresholds, somatosensory evoked potential amplitudes, and functional MRI activations under specific somatosensory stimulation conditions were measured. RESULTS: All patients demonstrated comparable results, revealing disrupted threshold detection to vibrotactile stimuli in the presence of a concurrent competing, contralateral input. In contrast, threshold detection was comparable between the affected and unaffected sides when there were no competing stimuli. This compromised capacity to inhibit competing sensory inputs was paralleled by a reduction in the measured activation of cortical representation in the stroke-affected hemisphere (functional MRI and somatosensory evoked potential) during bilateral stimulation. After recovery, perceptual detection improvements during bilateral stimulation were paralleled by enhancements of primary somatosensory cortical activation in the stroke-affected hemisphere. CONCLUSIONS: These results provide insight into potential mechanisms that contribute to sensory gating and suggest that the ability to control sensory input through effective gating mechanisms, in addition to primary somatosensory representation, may be important for poststroke sensory recovery.

Aged↗