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UBC Theses and Dissertations

Tactile gating in a reaching and grasping task reveals sensory and motor interactions affecting tactile sensitivity of the moving upper limb Colino, Francisco


A multitude of events bombard our sensory systems at every moment of our lives. Thus, it is important for the sensory cortex to gate unimportant events. Tactile suppression is a well-known phenomenon defined as a reduced ability to detect tactile events on the skin before and during movement. Previous experiments (e.g., Chapman et al., 1987) found detection rates decrease just prior to and during finger abduction, and decrease according to the proximity of the tactile event to the moving effector. However, there is no consensus regarding the cause of tactile gating. Previous work debated between centrally- vs. peripherally generated mechanisms causing tactile gating under different circumstances resulting in a reasonably good understanding of contributing neural networks. The present dissertation examined how tactile detection changes during a reach to grasp task. In a series of experiments, participants were asked to reach and grasp a cylinder. Tactors were attached to the index finger, the fifth digit and the forearm of both the right and left arm and vibrated at various epochs relative to an imperative “go” tone. These stimulation times were then renormalized post-hoc relative to movement onset. Movement performance was recorded using an infrared camera system tracking infrared emitting diodes. Results showed that detection rates at the forearm decreased before movement onset; whereas at the right index finger, right fifth digit and at the left index finger, left fifth digit and forearm sites no such reduction was observed (participants only moved the right upper limb). These results indicate that the task affects gating dynamics in a temporally- and contextually-dependent manner and implies that feedforward motor planning processes can modify sensory signals shifting the response criterion so that the likeliest response is negative.

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