Direct visuomotor mapping for fast visually-evoked arm movements

Area of Science:

• Neuroscience
• Motor Control
• Visuomotor Processing

Background:

• Saccadic reaction times (RTs) are fast and choice-invariant, attributed to sub-cortical eye movement circuitry.
• This involves direct retinal input to motor output mapping in the superior colliculus.
• It remains unclear if similar mechanisms govern rapid upper limb responses.

Purpose of the Study:

• To investigate if choice-invariance observed in eye movements extends to fast visuomotor responses of the upper limb.
• To explore the underlying neural pathways for rapid upper limb visual control.

Main Methods:

• A target-pointing paradigm was employed to measure upper limb reaction times.
• The number of possible target choices was systematically varied (1 to 4).
• A condition with altered stimulus-response mapping was introduced to assess choice costs.

Main Results:

• Very fast upper limb reaction times (<150 ms) were observed.
• Reaction times remained unaffected by increasing target choices from 1 to 4.
• Altering stimulus-response mapping increased RT and introduced a choice cost.

Conclusions:

• Fast upper limb visuomotor responses exhibit choice-invariance, similar to saccadic eye movements.
• These findings support a direct sub-cortical pathway for visual control of the upper limb.
• This pathway likely involves direct visual input to motor output mapping, bypassing cortical areas.