Contributions of MT and LIP to Perceptual Decision-Making: Systematic Comparison of Different Manipulation Methods

Decision-making involves multiple neural processes across many different brain areas.In perceptual decisionmaking, the middle temporal area (MT) and lateral intraparietal area (LIP) are important.Brain activity needs to be manipulated to understand the causal role of a brain area.Past studies have used varied task designs with only one method of manipulation applied to a single brain area, making it extremely difficult to pinpoint the precise contribution of a given area.We performed an analysis, examining twelve studies involving different types of neural manipulation within the same motion discrimination task.We examined four different types of neural manipulation: microstimulation, lesions, reversible inactivation, and optogenetics.We found that the results of the reviewed studies are most compatible with the following.The effects of manipulations are much larger for MT than for LIP.This suggests that MT provides the primary input for decision-making, whereas LIP refines the resulting saccadic eye movement to allow saccades to a specific visual field region.We also found that microstimulation is the most robust mode of manipulation, perhaps because it provides inputs to neurons that carry the most informative signals.This paper highlights the importance of adopting similar experimental designs to understand causal roles.