Biology subjects

Shadlen, M. N.

Publications and source records attributed to Shadlen, M. N..

5 recordsLinked to original sources

bioRxiv2018

Focal optogenetic suppression in macaque area MT biases direction discrimination and choice confidence, but only transiently

Insights from causal manipulations of brain activity depend on targeting the spatial and temporal scale most relevant for behavior. Using a sensitive perceptual decision task in monkeys, we examined the effects of randomly-interleaved, rapid, reversible inactivation on a spatial scale previously achieved only with electrical microstimulation. Inactivating neurons in area MT with consistent direction tuning produced systematic effects on choice and confidence. Behavioral effects were attenuated over the course of each session, suggesting compensatory adjustments in the downstream readout of MT over tens of minutes. Compensation also occurred on a sub-second time scale: behavior was largely unaffected on trials with visual stimuli (and concurrent suppression) longer than [~]350ms. These trends were similar for choice and confidence, consistent with the idea of a common mechanism underlying both measures. The findings demonstrate the utility of hyperpolarizing opsins for linking neural population activity at fine spatial and temporal scales to cognitive functions in primates.

neuroscience↗

bioRxiv2018

Value-based decisions involve sequential sampling from memory

Deciding between two equally appealing options can take considerable time. This observation has puzzled economists and philosophers, because more deliberation only delays the reward. Here we show that this seemingly irrational behavior is explained by the constructive use of memory. Using functional brain imaging in humans, we show that how long it takes to decide between two familiar food items is related to activity in the hippocampus, within specific regions shown to be associated with the retrieval of long-term memories. Moreover, we show that value is partially constructed during deliberation to resolve preference, and this constructive process changes behavior and brain responses. These results render memory as a supplier of evidence in value-based decisions, resolving a central paradox of choice.

animal behavior and cognition↗

bioRxiv2017

Counterfactual reasoning underlies the learning of priors in decision making

Accurate decisions require knowledge of prior probabilities (e.g., prevalence or base rate) but it is unclear how prior probability is learned in the absence of a teacher. We hypothesized that humans could learn base rates from experience making decisions, even without feedback. Participants made difficult decisions about the direction of dynamic random dot motion. For each block of 15-42 trials, the base rate favored left or right by a different amount. Participants were not informed of the base rate, yet they gradually biased their choices and thereby increased accuracy and confidence in their decisions. They achieved this by updating knowledge of base rate after each decision, using a counterfactual representation of confidence that simulates a neutral prior. The strategy is consistent with Bayesian updating of belief and suggests that humans represent both true confidence, that incorporates the evolving belief of the prior, and counterfactual confidence that discounts the prior.

neuroscience↗

bioRxiv2017

Comparison of decision-related signals in sensory and motor preparatory responses of neurons in Area LIP

Neurons in the lateral intraparietal area (LIP) of Macaques exhibit both sensory and oculomotor preparatory responses. During perceptual decision making, the preparatory responses have been shown to track the state of the evolving evidence leading to the decision. The sensory responses are known to reflect categorical properties of visual stimuli, but it is not known if these responses also track evolving evidence. We compared sensory and oculomotor-preparatory responses in the same neurons during a direction discrimination task when either the discriminandum (random dot motion) or an eye movement choice-target was in the neurons response field. Both configurations elicited task related activity, but only the motor preparatory responses reflected evidence accumulation. The results are consistent with the proposal that evolving decision processes are supported by persistent neural activity in the service of actions or intentions, as opposed to high order representations of stimulus properties.\n\nSIGNIFICANCE STATEMENTPerceptual decision making is the process of choosing an appropriate motor action based on perceived sensory information. Association areas of the cortex play an important role in this sensory-motor transformation. The neurons in these areas show both sensory- and motor-related activity. We show here that, in the macaque parietal association area LIP, signatures of the process of evidence accumulation that underlies the decisions are predominantly reflected in the motor-related activity. This finding supports the proposal that perceptual decision making is implemented in the brain as a process of choosing between available motor actions rather than as a process of representing the properties of the sensory stimulus.

neuroscience↗

bioRxiv2016

Cause for pause before leaping to conclusions about stepping

Many neurons in parietal and prefrontal association cortex undergo gradual changes in firing rate during the formation of some perceptual decisions. These dynamics are often ramp-like increases or decreases depending on the sign and strength of the sensory evidence and are thus hypothesized to represent the accumulation of noisy samples of evidence, analogous to biased diffusion. This idea was challenged recently. An analysis of sequences of action potentials recorded from neurons in the lateral intraparietal cortex (area LIP) suggests that the spikes on single trials are explained by rates that undergo a discrete step from an intermediate rate to either a low or high rate at a random time during deliberation. The average of such steps, like the average of biased diffusion, is consistent with the ramp-like firing rates observed in LIP, but a Bayesian model comparison deemed stepping superior. Here we show that a shortcoming in the mathematical depiction of drift-diffusion led to a severe bias in the model comparison. We conclude that at present there is no compelling evidence that favors the stepping account.

neuroscience↗