Corpus callosal microstructure influences intermanual transfer in chimpanzees

Abstract

Learning a new motor skill with one hand typically results in performance improvements in the alternate hand. The neural substrates involved with this skill acquisition are poorly understood. We combined behavioral testing and non-invasive brain imaging to study how the organization of the corpus callosum was related to intermanual transfer performance in chimpanzees. Fifty-three chimpanzees were tested for intermanual transfer of learning using a bent-wire task. Magnetic resonance and diffusion tensor images were collected from 39 of these subjects. The dominant hand showed greater performance benefits than the nondominant hand. Further, performance was associated with structural integrity of the motor and sensory regions of the CC. Subjects with better intermanual transfer of learning had lower fractional anisotropy values. The results are consistent with the callosal access model of motor programming.

Keywords: chimpanzees; fractional anisotropy; intermanual transfer; manual performance.

Figure 1

Curved metal rod used to test intermanual transfer of learning.

Figure 2

Subject removing the nut from the curved metal rod with the target hand. Note that the non-target hand is grasping the stationing stimulus.

Figure 3

Midsagittal section illustrating the subdivisions of the corpus callosum as determined by tractography. Region I (red) = prefrontal cortex; Region II (green) = premotor and supplementary motor cortices; Region III (yellow) = motor cortex; Region IV (blue) = sensory cortex; Region V (violet) = parietal, temporal and occipital cortices.

Figure 4

Callosal fiber projections from a single male chimpanzee, displayed from (A) dorsal, (B) sagittal, and (C) oblique views. Color distinguishes fibers projecting into cortical regions and are as follows: prefrontal (red), premotor and supplementary motor (green), motor (yellow), sensory (blue), and parietal, temporal and occipital (violet).

Figure 5

Subjects who trained on the nondominant hand (NDOM) showed greater intermanual transfer of learning than those trained on the dominant hand (DOM), as indicated by higher difference scores.