Can We Measure Brain Efficiency? An Empirical Test with Common Marmosets <b><i>(Callithrix jacchus)</i></b>

Abstract

Various measures of brain size correlate with cognitive performance; however, the fit is not perfect, which bears the question of whether brains also vary in efficiency. Such variation could be expected if a species faces constraints on brain enlargement, for example due to the impossibility of slowing down life history as a consequence of predator pressure, while simultaneously experiencing selective benefits from enhanced cognitive ability related to particular ecological or social conditions. Arguably, this applies to callitrichid monkeys and would lead to the prediction that their relatively small brains are particularly efficient in comparison to their sister taxa, Cebus. This study investigated whether callitrichids’ cognitive performance is better than would be expected given their brain size rather than comparing absolute performance between the taxa. As a measure of cognitive performance, we used the reversal learning paradigm, which is reliably and closely associated with brain size across primate taxa, and assessed performance in this paradigm (transfer index) in 14 common marmosets (Callithrix jacchus) as representatives of the callitrichids. These marmosets were found to show higher performance than would be expected for their brain size, and this relative performance was also higher than the relative performance in capuchin monkeys. We outline how these effects may be due to the cooperative breeding system of the callitrichids, particularly the enhancement of behavioural and cognitive propensities associated with shared care and provisioning.

Touchscreen assays of learning, response inhibition, and motivation in the marmoset (Callithrix jacchus)

“…This is somewhat contrary to current thinking regarding brain size and cognitive ability among nonhuman primates (see Deaner et al, 2007); however, marmosets have defied this correlation previously (Strasser and Burkart 2012). The present findings demonstrate that marmosets are certainly capable of engaging effectively in a touchscreen-based battery of behavioral assays.…”

The evolution of general intelligence

“…Differences in sensory-motor abilities and so on may well influence how difficult it is for a species to learn a particular discrimination. However, the crucial test is applied only once a specific criterion has been reached, and at least in marmosets, the time needed to achieve this criterion does not predict performance in the reversal trials (Strasser & Burkart 2012). Furthermore, it is reassuring that the strongest association between a specific task and G in Deaner et al (2006) was the one between reversal learning and G .…”

Reconsidering the evolution of brain, cognition, and behavior in birds and mammals

“…In primates, the Pearson correlation test between residuals from the regression of an estimate of general cognitive ability onto the size of the brain on one side, onto encephalization residuals calls for further studies ( t = 1.9854, df = 21, p -value = 0.06032, cor = 0.4, psychological data from Deaner et al, 2006). Notwithstanding the fact that the precision of the data is critically small and that many factors other than structure size control cognitive abilities (see sections Brain and Cognition; Species Differences in Cognition and Behavior), one of the reasons for this mixed result is the possibility that the size constraint has selected for mechanisms that increase brain efficiency in species with relatively small brains (Strasser and Burkart, 2012). A related hypothesis is that species that have undergone a decrease in brain size (see Montgomery et al, 2010) have kept some of the anatomical or physiological mechanisms evolved by their ancestor to counter the constraints of brain size (this could be an important factor in understanding the technology of the small brained Homo floresiensis , see for example Morwood et al, 2005).…”