On-Line Control of Grasping Actions: Object-Specific Motor Facilitation Requires Sustained Visual Input

Abstract

Dorsal stream visual processing is generally considered to underlie visually driven action, but when subjects grasp an object from memory, as visual information is not available, ventral stream characteristics emerge. In this study we use paired-pulse transcranial magnetic stimulation (TMS) to investigate the importance of the current visual input during visuomotor grasp. Previously, the amplitude of the paired-pulse motor evoked potentials (MEPs) in hand muscles before movement onset have been shown to predict the subsequent pattern of muscle activity during grasp. Specific facilitation of paired-pulse MEPs may reflect premotor-motor (PMC-M1) cortex connectivity. Here we investigate the paired-pulse MEPs evoked under memory-cued and visually driven conditions before grasping one of two possible target objects (a handle or a disc). All trials began with a delay period of 1200 ms. Then, a TMS pulse served as the cue to reach, grasp and hold the target object for 0.5 s. Total trial length was 5 s. Both objects were continually visible in both conditions, but the way in which the target object was designated differed between conditions. In the memory-cued condition, the target object was illuminated for the first 200 ms of the trial only. In the visually driven condition, the target object was illuminated throughout the 5 s trial. Thus, the conditions differed in whether or not the object to be grasped was designated at the time of movement initiation. We found that the pattern of paired-pulse MEP facilitation matched the pattern of object-specific muscle activity only for the visually driven condition. The results suggest that PMC-M1 connectivity contributes to action selection only when immediate sensory information specifies which action to make.

Anticipating the course of an action: Evidence from corticospinal excitability

“…Our results are consistent with observations from previous studies suggesting that excitatory inputs to M1 are modulated during motor preparation [23,24]. Those studies indicated that there were object-and musclespecific changes in the cortical excitability of M1 immediately before a participant grasped an object.…”

“…context or task dependent) [17,22]. Like single-pulse TMS, pairedpulse TMS has been shown to be a sensitive method to measure cortico-cortical interactions, and has been used successfully in experiments assessing the excitability of circuits intrinsic to the cerebral cortex itself [23,24].…”

“…Also known as short intracortical facilitation (SICF), this effect seems to be partially due to interactions between I waves and is thought to take place in the motor cortex or upstream from the cortico-spinal neuron [23][24][25]. Cattaneo and colleagues demonstrated that there is an enhancement in the excitability of those inputs to the corticospinal neurons projecting from the motor cortex to the specific muscles to be used during grasping actions at least 600 ms before the movement itself takes place.…”

Amyotrophic lateral sclerosis—Evolutionary and other perspectives

“…The M1 receives two major inputs. [41][42][43] One is from the supplementary motor cortex (SMA) and presupplementary motor cortex (preSMA), which in turn receives inputs from the basal ganglia and prefrontal cortex. This circuit is mainly involved in decisionmaking movement.…”

A system for sensory motor rehabilitation of the upper limb with virtual reality, exoskeleton robot, and real objects

“…Modulation of sensory experience appears to influence performance of healthy humans [132], some patients [76], and the aging [133], and when sensory modulation is a benefit above real world experiences [134]. Visual experience of real objects engages important neural regions involved with recognition of the objects, properties, and location in space, and provides for online correction of movement [23,101,[135][136][137][138]. Postural, visual, tactile, and other sensory experiences modulate sensory fields important for responding accurately to stimuli, and inform the nervous system of body position in peripersonal space relevant when moving about and interacting with real world objects [26,83,127,132].…”