We have also examined handedness for a number of natural behaviors by the chimpanzees including scratching, grooming, throwing and locomotion (pics for these three actions).   The goal of these studies has been to examine whether chimpanzees show population-level handedness for these different tasks and to assess the role of genetic and non-genetic factors on the development and expression of handedness.  In addition, these data serve as measures to correlate with neuroanatomical asymmetries obtained from the MRI scans (described below).

In addition to the handedness test, we have also been examining the cognitive foundations of gestural and vocal communication in the chimpanzees.  In collaboration with Dr. Dave Leavens at the University of Sussex (link) and Autumn Hostetter now at Kalamazoo College, we have conducted a series of studies examining the frequency and function of gestural and vocal communication in chimpanzees during interspecies communication tasks.   Specifically, we have examined the influence of human attentional states on the use of manual, auditory and tactile gesture by the chimpanzees.   One of the more interesting observation to emerge form this work was the documentation of the use of two distinct novel sounds, referred to as the “raspberry” (link) and “extended food grunt” (link) that the chimpanzee use to capture the attentionl of an otherwise inattentive human audience.   Interestingly, when producing these sounds the chimpanzees show a rightward oro-facial asymmetry in the facial musculature that suggest that the left half of the brain is controlling the movements of these actions.

Figure 1

Figure 1. Significant Areas of Activation for Communicative Production
Measurements refer to the depth from the dorsal tip of the brain (z, dorsal to ventral), distance from frontal pole (y, anterior to posterior), or distance from midsagittal (x, ascending positive values correspond to the right hemisphere, medial to lateral; ascending negative values correspond to the left hemisphere, medial to lateral). Panels display axial (A), coronal (B), and sagittal (C) views of MR images with significant GV > BL activation. Numbers correspond to the following anatomical locations: 1, bilateral superior frontal gyrus; 2, left inferior frontal gyrus (depicted in large bold type); 3, bilateral posterior cingulate gyrus; 4, left caudate/putamen; 5, left medial pre- and postcentral gyrus; 6, left frontal orbital gyrus; 7, left thalamus; 8, right middle temporal gyrus; 9, right middle frontal gyrus. Note that not all areas of activation are labeled in all planes. See Table 1 for a complete list of regions with significant GV > BL activation.

Figure 2

Figure 2. Significant Lateralized Activation
The average comparison volume (GV > BL) from all three subjects was flipped on the x axis (i.e., right-left) and then subtracted from the correctly oriented volume. A t map volume was then calculated from this subtracted volume (see the Experimental Procedures) and significant areas of activation identified, t R 4.31. Values indicate significantly lateralized activity in that hemisphere (i.e., cluster in RH of brain indicates right hemisphere activation is greater than activation in corresponding area in the left hemisphere).

Lastly, our laboratory is currently engaged in a number of studies examining physical and social cognition in the chimpanzees with the long term goal to be able to assess individual differences and to evaluate the influence of sex and rearing history variables on cognitive performance.   These studies involve the use of structured tasks to measure discrimination performance, memory, spatial cognition, numerical cognition, gaze following, attribution of mental state and imitation.  There are also ongoing studies assessing delayed gratification, self-recognition and social learning in the laboratory.

Structural and Functional Imaging of the Chimpanzee Brain

Over the past 10 years, our laboratory has obtained a relatively large sample of MRI scans in chimpanzees (n > 100) as well as smaller data sets in bonobos (n = 7), orangutans (n = 11) and gorillas (n = 6).   From the MRI scans, we have been assessing whether chimpanzees (and other great apes) show a) population-level asymmetries in specific brains areas and b) whether variation in different brains areas correlate with specific motor or cognitive functions.  Of particular interest has been whether chimpanzees show asymmetries in the so-called homologs to the human language centers, including Broca’s and Wernicke’s area.   In chimpanzees, these regions correspond to the inferior frontal gyrus (IFG) (axial view, sagittal view) and planum temporale (sagittal view, coronal view).  In the chimpanzees, significant population-level leftward asymmetries have been found for both the IFG and PT.   Other brain areas of interest have included the prefrontal cortex, hippocampus, amygdala, fusiform gyrus, planum parietale, basal ganglia and corpus callosum.

More recently, we have conducted functional imaging in chimpanzees using PET when they have performed different motor or perceptual tasks including grasping, gesture-vocal communication and auditory perception of species-specific sounds.  In these studies, we use FDG as the ligand and the chimpanzees perform a task during the uptake period of the FDG.  We then temporarily anesthetize the apes and image the brain after the ligand has been absorbed to assess whether the FDG has been taken up in the brain.  Our results to date suggest that chimpanzee show leftward asymmetries in the caudate and inferior frontal gyrus when using gestures and vocalizations to communicate (picture).

Cellular Asymmetries in Relation to Morphology

Lastly, in collaboration with Dr. Chet Sherwood at George Washington University (link), we have been evaluating the relationship between behavior, neuroanatomical morphology and cellular organization. When chimpanzees die from natural causes, we have arranged to obtain their brains at post-mortem.  The post-mortem brains are fixed in formalin and subsequently scanned with a high resolution scanner (7.0T).   The brains are then sent to Dr. Sherwood who then sections the brain and performs a series of serological analyses to assess cellular organization within brain regions of interest.  The cellular asymmetries are then correlated with variation in the morphological region of interest as well as the subjects behavioral data (if available).   We are currently assessing variation in the organization and distribution of Brodmann’s area 44 and 45 cells in the IFG of the chimpanzee brain.  In our previous studies, we have examined variation in the motor-hand area of the precentral gyrus of the chimpanzees and have found significant association between handedness and asymmetries in the density of layer II/III paravalbumin-immunoreactive interneurons.  We also found that across all chimpanzees, there was a significant leftward asymmetry in the density of neurons in layer II/III.