Separable Learning Systems in the Macaque Brain and the Role of Orbitofrontal Cortex in Contingent Learning

Abstract

SummaryOrbitofrontal cortex (OFC) is widely held to be critical for flexibility in decision-making when established choice values change. OFC's role in such decision making was investigated in macaques performing dynamically changing three-armed bandit tasks. After selective OFC lesions, animals were impaired at discovering the identity of the highest value stimulus following reversals. However, this was not caused either by diminished behavioral flexibility or by insensitivity to reinforcement changes, but instead by paradoxical increases in switching between all stimuli. This pattern of choice behavior could be explained by a causal role for OFC in appropriate contingent learning, the process by which causal responsibility for a particular reward is assigned to a particular choice. After OFC lesions, animals' choice behavior no longer reflected the history of precise conjoint relationships between particular choices and particular rewards. Nonetheless, OFC-lesioned animals could still approximate choice-outcome associations using a recency-weighted history of choices and rewards.

Separate value comparison and learning mechanisms in macaque medial and lateral orbitofrontal cortex

“…This fact, together with the absence of group difference in preoperative performance, meant direct comparisons could be made between mOFC lesions in the current experiment ( Fig. 2B) and lOFC lesions (9) (Fig. 2, Insets).…”

“…S2). The schedules were identical to ones used to identify impairments in credit assignment after lOFC lesion (9). This fact, together with the absence of group difference in preoperative performance, meant direct comparisons could be made between mOFC lesions in the current experiment ( Fig.…”

“…The investigation of value learning focused on credit assignment: the process by which visual stimuli are associated with reward values during associative learning (9). Normally, monkeys learn to attribute value to a stimulus as a function of the precise history of reward received in association with the choice of that particular stimulus.…”

“…We compared the effects of mOFC lesions with previously published effects of lOFC lesions (9). All other data and analyses are uniquely presented here.…”

The role of learning-related dopamine signals in addiction vulnerability

“…In support, Takahashi et al (2011) have recently shown that cocaine interferes with the ability of the orbitofrontal cortex to establish detailed state-space (Walton et al, 2010), which would lead to less accurate models and hence less accurate predictions. In the VOI account, increased cost of computation would have very similar effects, and cognitive impairments could be involved in the effect of stress (Schwabe and Wolf, 2009) and certainly the effect of dual tasks (Otto et al, 2013).…”