Attention and Age-Related Components of Visual-Tactile Modulation of Somatosensory Cortex and Motor Implications
Mader, Laura Beth
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Successful interaction with the external world requires continual sensory detection, sensorimotor translations and goal-directed motor execution. Attention to task-relevant stimulation can facilitate sensory detection and improve behavioural performance. Crossmodal visual and somatosensory interaction within early sensory regions appears to further enhance processing, but required stimulus congruency for optimal sensorimotor communication is relatively unknown. This thesis first investigates the impact of visual-tactile temporal presentation on somatosensory activation within healthy young adults. As expected, findings revealed simultaneous crossmodal stimulation to maximally augment tactile event-related potentials (ERPs). These results were subsequently applied to determine the influence of attentional or low-level priming effects on motor performance within young and older adults. The bulk of this thesis assesses whether crossmodal interaction is similarly influential across age. Task-relevant visual-tactile stimulation was predicted to facilitate sensory regions and improve motor behaviour for both young and older subjects. Visual distraction was expected to limit tactile processing and impair performance only within older subjects. Tactile (P50, P100, N140, P230) and visual (N1) ERPs were recorded from 32 channels while healthy young and older subjects preformed a sensory integration task. Three conditions varying in modality of stimulation (tactile/visual) and task relevancy (relevant/irrelevant) required subjects to attend to stimuli and make an appropriately graded motor response. Blocked training prior to collection ensured stimulus-response associations and task demands were learned. Individual ERPs were time-locked to the onset of the first or second stimulus and quantified at CP3, CP4, FCZ, O1 and O2. Despite evidence of age-dependent effects in tactile processing, grand average waveforms suggest older adults maintain the ability to selectively attend to task-relevant information. Improved motor accuracy was not associated with crossmodal facilitation in either age group, however results indicate that performance of older adults declines with visual distraction. Differential N1 modulation across age suggests younger adults disengage from visual distraction after initial saliency (earlier latency with second distractor), while older adults may use a conscious strategy to shift attention away from distraction (latency unchanged but reduced amplitude with second distractor). Overall, these results follow previous studies and suggest older adults compensate for a general increase in processing background information by altering performance strategy. This vulnerability to distraction appears to negatively impact motor performance even within healthy aged adults.