Representing tools as hand movements: early and somatotopic visuomotor transformations

Area of Science:

• Neuroscience
• Motor Control
• Cognitive Science

Background:

• Affordance links object properties to possible interactions.
• Canonical neurons in monkeys link visual and motor object features.
• Early human visuomotor transformations for specific affordances remain unclear.

Purpose of the Study:

• Investigate early cortico-spinal facilitation and hand synergies from tool observation.
• Determine if visual features of specific affordances induce early visuomotor transformations in humans.

Main Methods:

• Used an adaptation-stimulation paradigm with passive observation of finger movements.
• Adapted neuronal populations for precision or power grip actions.
• Applied Transcranial Magnetic Stimulation (TMS) to the motor cortex 150ms after tool image presentation.

Main Results:

• Cortico-spinal excitability showed modulations matching tool affordances.
• TMS-induced hand movements displayed grip-specific whole-hand synergies.
• Early visuomotor transformation emerged rapidly upon tool observation.

Conclusions:

• Direct proof of early visuomotor transformation when observing tools.
• Motor details in observed tool affordances match those in performed actions.
• Human visuomotor system processes tool affordances with high specificity and early onset.