Broca's area and chimpanzee communication

Chimpanzees use their own version of Broca's area when they communicate, according to a new PET scan study by Jared Taglialatela and colleagues. The 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 [1], [2] and [3]. 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.

I wrote a couple of years ago about the Broca's area homolog in macaques, and the involvement of the area in planning time-sensitive action sequences in people. Those studies clearly foreshadowed the current result, since they provide both a phylogenetic expectation that this brain area evolved early in anthropoid evolution (or earlier), and the functional expectation that motor sequences characteristic of communication depend on it.

There is some uncertainty in the current analysis, because the PET scanning method doesn't localize the increased activity as tightly as they would like:

Although these data indicate that the left IFG is involved in the production of communicative signals in chimpanzees, cytoarchitectonically, it is not clear what cell types fully comprise this region [36]. Therefore, it is not possible to determine whether or not the neuronal metabolic activity reported in this study corresponds to an area within the chimpanzee IFG that contains Brodmann's area 44/45 cells -- those cells that comprise Broca's area in humans. In fact, additional areas of significant activation are observed in the frontal orbital gyrus and the frontal pole (Figure 2). Additional work is needed to explore the significance of these areas of activation.

Nice piece of work. I wouldn't want to be the one to get a chimp into a scanner...

References:

Taglialatela JP, Russell JL, Schaeffer JA, Hopkins WD. 2008. Communicative signaling activates 'Broca's' homolog in chimpanzees. Curr Biol 18:1-6. doi:10.1016/j.cub.2008.01.049