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, 18 (5), 343-8

Communicative Signaling Activates 'Broca's' Homolog in Chimpanzees

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Communicative Signaling Activates 'Broca's' Homolog in Chimpanzees

Jared P Taglialatela et al. Curr Biol.

Abstract

Broca's area, a cerebral cortical area located in the inferior frontal gyrus (IFG) of the human brain, has been identified as one of several critical regions associated with the motor planning and execution of language. Anatomically, Broca's area is most often larger in the left hemisphere, and functional imaging studies in humans indicate significant left-lateralized patterns of activation during language-related tasks. If, and to what extent, nonhuman primates, particularly chimpanzees, possess a homologous region that is involved in the production of their own communicative signals remains unknown. Here, we show that portions of the IFG as well as other cortical and subcortical regions in chimpanzees are active during the production of communicative signals. These findings are the first to provide direct evidence of the neuroanatomical structures associated with the production of communicative behaviors in chimpanzees. Significant activation in the left IFG in conjunction with other cortical and subcortical brain areas during the production of communicative signals in chimpanzees suggests that the neurological substrates underlying language production in the human brain may have been present in the common ancestor of humans and chimpanzees.

Figures

Figure 1
Figure 1. Three-Dimensional Reconstructions of Magnetic Resonance Images of a Representative Chimpanzee Brain
(A) Illustrated is a three-dimensional-rendered MR image of chimpanzee brain cut in to reveal the axial view. “x” and “y” indicate the orthogonal planes (sagittal and coronal, respectively) referred to in Figure 2. Arrow directions refer to ascending slices displayed in Figure 2. (B) The z axis indicates the axial plane referred to in Figure 2.
Figure 2
Figure 2. Significant Areas of Activation for Communicative Production
PET activation (GV > BL) was overlaid on MR images of representative chimpanzee brain. “x,” “y,” and “z” refer to the planes described in Figure 1. 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 3
Figure 3. 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 ≥ 4.31. The figure depicts PET activation overlaid on MR images of representative chimpanzee brain. “x,” “y,” and “z” and corresponding values refer to the planes and the anatomical locations described in Figures 1 and 2. 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).

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