Modelling contralesional movement slowing after unilateral brain damage

Area of Science:

• Neuroscience
• Cognitive Psychology
• Motor Control

Background:

• Effective interaction with the environment necessitates rapid processing of relevant stimuli and organized motor responses.
• Unilateral brain lesions often impair motor behavior, particularly in the visual field opposite the lesion (contralesional space).
• Accumulator models offer frameworks to differentiate between slowed evidence accumulation and increased evidence thresholds as causes of motor deficits.

Purpose of the Study:

• To investigate the functional cause of motor response slowing in patients with unilateral right hemisphere damage.
• To determine whether slowed evidence extraction or an increased evidence threshold underlies contralesional motor deficits.

Main Methods:

• Three patients with unilateral right hemisphere lesions participated.
• A visually guided saccade task was employed to measure response latencies.
• Saccade latency distributions were analyzed using competing accumulator models.

Main Results:

• All patients exhibited significantly increased response latencies for targets in the contralesional visual field.
• Model fitting indicated that the observed latency differences were best explained by an elevated evidence threshold.
• The data did not support slowed evidence extraction as the primary cause.

Conclusions:

• Right hemisphere damage leads to motor response deficits in contralesional space primarily through an increased requirement for response evidence.
• This finding has implications for understanding sensorimotor integration and the neural basis of response selection.