Grey squirrels (Sciurus carolinensis) show a feature-negative effect specific to social learning.

Previous laboratory studies on social learning suggest that some animals can learn more readily if they first observe a conspecific demonstrator perform the task unsuccessfully and so fail to obtain a food reward than if they observe a successful demonstrator that obtains the food. This effect may indicate a difference in how easily animals are able to associate different outcomes with the conspecific or could simply be the result of having food present in only some of the demonstrations. To investigate we tested a scatter-hoarding mammal, the eastern grey squirrel, on its ability to learn to choose between two pots of food after watching a conspecific remove a nut from one of them on every trial. Squirrels that were rewarded for choosing the opposite pot to the conspecific chose correctly more frequently than squirrels rewarded for choosing the same pot (a feature-negative effect). Another group of squirrels was tested on their ability to choose between the two pots when the rewarded option was indicated by a piece of card. This time, squirrels showed no significant difference in their ability to learn to choose the same or the opposite pot. The results add to anecdotal reports that grey squirrels can learn by observing a conspecific and suggest that even when all subjects are provided with demonstrations with the same content, not all learning occurs equally. Prior experience or expectations of the association between a cue (a conspecific) and food influences what can be learned through observation whilst previously unfamiliar cues (the card) can be associated more readily with any outcome.

Audience effects on food caching in grey squirrels (Sciurus carolinensis): evidence for pilferage avoidance strategies.

If food pilferage has been a reliable selection pressure on food caching animals, those animals should have evolved the ability to protect their caches from pilferers. Evidence that animals protect their caches would support the argument that pilferage has been an important adaptive challenge. We observed naturally caching Eastern grey squirrels (Sciurus carolinensis) in order to determine whether they used any evasive tactics in order to deter conspecific and heterospecific pilferage. We found that grey squirrels used evasive tactics when they had a conspecific audience, but not when they had a heterospecific (corvid) audience. When other squirrels were present, grey squirrels spaced their caches farther apart and preferentially cached when oriented with their backs to other squirrels, but no such effect was found when birds were present. Our data provide the first evidence that caching mammals are sensitive to the risk of pilferage posed by an audience of conspecifics, and that they utilise evasive tactics that should help to minimise cache loss. We discuss our results in relation to recent theory of reciprocal pilferage and compare them to behaviours shown by caching birds.

Autonomic arousal in an appetitive context in primates: a behavioural and neural analysis.

Central to many emotional responses is the accompanying peripheral somatic and autonomic arousal, feedback from which has been hypothesized to enhance emotional memory and to contribute to appraisal processes and decision making, and dysfunction of which may contribute to antisocial behaviour. Whilst peripheral arousal may accompany both positive and negative emotional contexts, its relationship with the former is poorly understood, as are the neural mechanisms underlying such a relationship. The purpose of the present study was to determine the autonomic correlates of anticipation, as well as consumption, of high incentive food, in the freely moving common marmoset and to investigate the contribution of the amygdala to such effects. Blood pressure (BP) and heart rate (HR) were measured remotely by a telemetric device implanted into the descending aorta and behavioural responses were monitored whilst marmosets viewed preferred or non-preferred foods and were then allowed access to eat those foods. A marked rise in blood pressure in unrestrained marmosets was observed in response both to the sight of highly preferred foods (anticipatory period) as well as during the actual consumption of those foods (consummatory period). Excitotoxic lesions of the amygdala abolished the autonomic arousal in the anticipatory period, but spared both the behavioural arousal in the anticipatory period and the autonomic arousal in the consummatory period. Together these data serve as an important step towards understanding the role of autonomic arousal in emotion and its neural underpinnings.

Lesions of the orbitofrontal but not medial prefrontal cortex disrupt conditioned reinforcement in primates.

The ventromedial prefrontal cortex (PFC) is implicated in affective and motivated behaviors. Damage to this region, which includes the orbitofrontal cortex as well as ventral sectors of medial PFC, causes profound changes in emotional and social behavior, including impairments in certain aspects of decision making. One reinforcement mechanism that may well contribute to these behaviors is conditioned reinforcement, whereby previously neutral stimuli in the environment, by virtue of their association with primary rewards, take on reinforcing value and come to support instrumental action. Conditioned reinforcers are powerful determinants of behavior and can maintain responding over protracted periods of time in the absence of and potentially in conflict with primary reinforcers. It has already been shown that conditioned reinforcement is dependent on the amygdala, and because the amygdala projects to both the orbitofrontal cortex and the medial PFC, the present study determined whether conditioned reinforcement was also dependent on one or the other of these prefrontal regions. Comparison of the behavioral effects of selective excitotoxic lesions of the PFC in the common marmoset revealed that orbitofrontal but not medial PFC lesions disrupted two distinct measures of conditioned reinforcement: (1) acquisition of a new response and (2) sensitivity to conditioned stimulus omission on a second-order schedule. In contrast, the orbitofrontal lesion did not affect sensitivity to primary reinforcement as measured by responding on a progressive-ratio schedule and a home cage consumption test. Together, these findings demonstrate the critical and specific involvement of the orbitofrontal cortex but not the medial PFC in conditioned reinforcement.