Elsevier

Neuroscience Letters

Volume 518, Issue 2, 19 June 2012, Pages 172-175
Neuroscience Letters

Curious monkeys have increased gray matter density in the precuneus

https://doi.org/10.1016/j.neulet.2012.05.004Get rights and content

Abstract

Curiosity is a cornerstone of cognition that has the potential to lead to innovations and increase the behavioral repertoire of individuals. A defining characteristic of curiosity is inquisitiveness directed toward novel objects. Species differences in innovative behavior and inquisitiveness have been linked to social complexity and neocortical size [18]. In this study, we observed behavioral actions among nine socially reared and socially housed capuchin monkeys in response to an unfamiliar object, a paradigm widely employed as a means to assess curiosity. K-means hierarchical clustering analysis of the behavioral responses revealed three monkeys engaged in significantly more exploratory behavior of the novel object than other monkeys. Using voxel-based-morphometry analysis of MRIs obtained from these same subjects, we demonstrated that the more curious monkeys had significantly greater gray matter density in the precuneus, a cortical region involved in highly integrated processes including memory and self-awareness. These results linking variation in precuneus gray matter volume to exploratory behavior suggest that monitoring states of self-awareness may play a role in cognitive processes mediating individual curiosity.

Highlights

► We examine the neural correlates of curiosity. ► Curious monkeys had a greater density of gray matter in the precuneus. ► The precuneus is associated with integrated tasks such as memory and self-awareness. ► Monitoring self-awareness may play a role in cognitive processes mediating curiosity.

Introduction

Curiosity is the desire to learn about what is unknown. Montgomery [15], [16] postulated that human and animal behavior is often motivated by such self-enrichment tendencies. His approach-avoidance theory maintained that curiosity is a balance between two motivations—the drive to explore and the fear resulting from the novel situation. Berlyne [5] considered curiosity to be a motivational drive, and a prerequisite for exploratory behavior. The motivation for curiosity is unique from other drives in that it is aroused not by an internal state in the individual, but rather by a novel external stimulus. This motivation is also satiated quickly with continuous exposure to the stimulus.

Curiosity and exploratory behavior are intertwined and as such, difficult to define independently; both terms are used to refer to behavior that provides a gain in information about the environment.

The neurobiology underlying curiosity remains poorly understood. In humans, curiosity has been linked to functional activation in the inferior frontal gyrus (Broca's area) and the caudate nucleus, associated with anticipated reward [13]. Dopaminergic receptors in the dentate gyrus are associated with the generation of exploratory behavior in mice [20]; these receptors also play a role in learning and memory.

Here, we characterized behavioral responses among nine socially reared and socially housed capuchin monkeys to a novel object, a paradigm widely employed as a means to assess curiosity [8], [17], [25]. Additionally, we obtained high-resolution T1-weighted structural magnetic resonance images of the brain from these same monkeys, to relate neuroanatomical differences to their behavior.

Section snippets

Subjects

Nine adult capuchin monkeys (Cebus apella) were used in this study, including five males and four females ranging in age from 5 to 23 years (M = 13.4 years, SD = 6.6 years). Subjects were socially housed in enriched environments with perches, swings, and fresh browse. The social composition of this group closely resembled that of wild groups; furthermore, normative capuchin social behavior–including grooming and playing—was regularly displayed. New World Monkey Chow and water were available ad

Results

Video recordings of the test session were scored by an individual who was unfamiliar with the subjects. The following data were recorded for each subject: latency to first approach the object and the total number of exploratory actions of different types during the 5-min testing session. [A complete description of the scoring procedure can be found in Supplement.] Exploratory behavior toward the object consisted of any of the following behaviors:

  • a)

    tactile exploration—touching, grabbing, climbing

Discussion

In the current study, highly curious monkeys had a greater density of gray matter in the precuneus than the less curious monkeys. To our knowledge, this is the first investigation concerning the neural basis of variation in curiosity amongst individuals, and the first investigation to indicate that the precuneus is involved in curiosity. The precuneus plays a central role in highly integrated tasks in humans including episodic and semantic memory, and self-awareness [6], [7]. Our results

Acknowledgements

We thank our veterinary and laboratory staff for assistance on the project, and the staff of the Neuroscience Imaging Center.

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