Handedness for tool use correlates with cerebellar asymmetries in chimpanzees (Pan troglodytes).

Abstract

Recent studies have shown that great ape species possess patterns of macrostructural neocortical asymmetries that are similar to those found in humans. However, little is known about the asymmetry of subcortical structures in great apes. To address this lack of data, the authors assessed left-right asymmetry of the anterior and posterior aspects of cerebellum from MRI brain scans of 53 chimpanzees (Pan troglodytes). No population-level bias was found for either the anterior or the posterior region of the cerebellum. However, a significant inverse association was found in the asymmetry quotients of the anterior and posterior regions, indicating that the cerebellum was torqued at the individual level. Additionally, handedness for tool use but not other measures was associated with variation in cerebellar asymmetries. Last, older chimpanzees had a smaller cerebellum after brain volume was adjusted for. The results are discussed in the context of brain changes in primate evolution related to tool use. Keywordscerebellum; torque; tool use; handedness; chimpanzee Over the last 5 years, an increasing body of evidence has shown the presence of macrostructural asymmetries in the great ape brain that closely resemble well-known patterns of asymmetry in the human brain Pilcher, Hammock, & Hopkins, 2001). Most of these studies have focused on the neocortex, particularly on regions believed to be homologous to cortical areas of the human brain involved in linguistic functions. For example, in great apes, as in humans, the sylvian fissure has been reported to be longer in the left hemisphere, particularly in its postcentral region Hopkins, Pilcher, & MacGregor, 2000;Yeni-Komshian & Benson, 1976). Similarly, leftward cortical asymmetries in great apes and humans have been reported for the planum temporale, an area located on the superior temporal gyrus, which coincides with part of Wernicke's area Correspondence concerning this article should be addressed to Claudio Cantalupo, Department of Psychology, Clemson University, Clemson, SC 29634. E-mail: ccantal@clemson.edu. Galaburda, 1995;Gannon, Holloway, Broadfield, & Braun, 1998;Gilissen, 2001;Hopkins, Marino, Rilling, & MacGregor, 1998). A number of studies have also reported leftward asymmetries in the frontal operculum in the inferior frontal lobe, commonly believed to contain part of Broca's area (Amunts et al., 1999;Cantalupo & Hopkins, 2001;Foundas, Eure, Luevano, & Weinberger, 1998), although the scope of this finding remains to be fully assessed (Sherwood, Broadfield, Holloway, Gannon, & Hof, 2003;Watkins et al., 2001). Some studies have revealed converging asymmetry patterns also in other regions of the great ape and human brain. For example, the great ape brain has been found to show the same frontal (right > left) and occipital (left > right) petalias, also known as developmental torque, consistently reported in the human literature (Holloway & De La Coste-Lareymondie, 1982;Hopkins & Marino, 2000;LeMay, 1976LeMay, , 1982LeMay, , 1985Pilcher et al., 2001). Fi...

The neural and cognitive correlates of aimed throwing in chimpanzees: a magnetic resonance image and behavioural study on a unique form of social tool use

“…The results from comparing right-and left-handed throwers also support this conclusion, because differences in WM are hemisphere-specific and contralateral to the preferred hand that the chimpanzees use for throwing. The association between hand preferences for throwing and asymmetries within the IFG and KNOB are also consistent with previous studies showing that handedness for other forms of tool use, such as simulated termite-fishing and nutcracking, is linked to lateralization in the cortical language area homologues of chimpanzees [33,44]. It should also be noted that asymmetries in hand use for manual gestures are associated with asymmetries within the IFG [45] Thus, the results reported here are consistent with the evolutionary hypothesis that throwing may have served as a preadaptation for the neural adaptation of motor programmes necessary for complex motor actions, including language and speech [11].…”

Bipedal tool use strengthens chimpanzee hand preferences

“…Various studies suggest that handedness in great apes may be linked to posture and/or tool use (Olson et al, 1990; Hopkins, 1993; Hopkins et al, 2007; Cantalupo et al, 2008). Several previous studies report a right-hand bias when in bipedal versus quadru-pedal posture in all four great ape species, but none of them directly examined bipedal tool use.…”

Volumetric and lateralized differences in selected brain regions of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus)

“…In studies of chimpanzees, we have previously found that variation in handedness for tool use, but not other motor actions, are associated with lateralization in the cerebellum [Cantalupo et al, 2008]. More recently, we have also found that chimpanzees who have learned to reliably throw have significantly larger cerebella than chimpanzees who do not throw, suggesting that experiential factors can influence the size of the cerebellum or alternatively, that certain patterns of neural organization within the cerebellum facilitate the acquisition of certain motor skills [Cantalupo & Hopkins, 2009].…”

“…Although the tracers were not blind to the species of the apes, they were blind to the hypotheses of the study. Before collection of the data, inter-rater reliability in the measurement of each brain region was established between two raters [Cantalupo et al, 2003, 2008; Freeman et al, 2004; Hopkins & Cantalupo, 2004]. To assess inter-rater reliability, two individuals measured all both brain regions for ten individual chimpanzees.…”