Parietal Cortex Flashcards
Perceptual decision making is easily conceived of as a
two-stage process in which a decision variable evolves until a stopping mechanism commits the process to a particular choice (Schall 2001)
Evidence that the lateral intra-parietal (LIP) cortex is involved in decision making first came from
studies demonstrating that neuronal firing in the LIP could predict the direction, timing and magnitude of saccadic eye movement in monkeys viewing random-dot motion for reward (RDM) (Shadlen and Newsome, 2001)
RDM direction discrimination was developed to study
the relationship between sensory encoding and perception
The RDM task requires
a single stimulus presentation and thus eliminates the need for working memory
The monkey decides between
two possible (opposite) directions of motion that are known in advance
Task difficulty is controlled by
varying the percentage of coherently moving dots.
The direction decision is typically indicated with
an eye movement (saccade)
When the visual stimulus was presented only briefly
LIP activity persisted for up to 800ms until a decision was made which corresponded to the saccade (Huk and Shadlen, 2005), indicating that the LIP is involved in time integration of the response
The spike rates of single LIP neurons have been interpreted as
direct neural correlates of an evolving decision variable (Gold & Shadlen 2007
Meanwhile, neuronal firing in the
middle temporal visual area (MT) have been implicated in representing the motion stimulus (Britten et al., 1993).
Together, these properties have given rise to a model where
LIP neurons either integrate, or reflect the integration of, motion evidence from area MT in favour of a decision
What opposes the model of LIP in decision making?
silencing the LIP does not impact decision making (Katz et al.,2016) suggests that direction-related signals in the LIP may be a result of feedback or extensive training.
