Genetic Factors and Orofacial Motor Learning Selectively Influence Variability in Central Sulcus Morphology in Chimpanzees (Pan troglodytes)

Abstract

Captive chimpanzees () have been shown to learn the use of novel attention-getting (AG) sounds to capture the attention of humans as a means of requesting or drawing their attention to a desired object or food. There are significant individual differences in the use of AG sounds by chimpanzees and, here, we examined whether changes in cortical organization of the central sulcus (CS) were associated with AG sound production. MRI scans were collected from 240 chimpanzees, including 122 that reliably produced AG sounds and 118 that did not. For each subject, the depth of CS was quantified along the superior-inferior plane with specific interest in the inferior portion corresponding to the region of the motor cortex where the mouth and orofacial movements are controlled. Results indicated that CS depth in the inferior, but not superior, portion was significantly greater in chimpanzees that reliably produced AG sounds compared with those who did not. Quantitative genetic analyses indicated that overall CS surface area and depth were significantly heritable, particularly in the superior regions, but less so in the inferior and central portions. Further, heritability in CS depth was altered as a function of acquisition of AG sounds. The collective results suggest that learning to produce AG sounds resulted in region-specific cortical reorganization within the inferior portion of the CS, a finding previously undocumented in chimpanzees or any nonhuman primate. Recent studies in chimpanzees () have shown that some can learn to produce novel sounds by configuring different orofacial movement patterns and these sounds are used in communicatively relevant contexts. Here, we examined the neuromorphological correlates in the production of these sounds in chimpanzees. We show that chimpanzees that have learned to produce these sounds show significant differences in central sulcus (CS) morphology, particularly in the inferior region. We further show that overall CS morphology and regions within the superior portion are significantly heritable, whereas central and inferior portions of the CS are not. The collective findings suggest chimpanzees exhibit cortical plasticity in regions of the brain that were central to the emergence of speech functions in humans.

Sulcal organization in the medial frontal cortex provides insights into primate brain evolution

“…and the chimpanzee brain, e.g., ref. 59 . Indeed, Hopkins et al 59 found that male chimpanzees producing attention getting sounds showed a larger leftward asymmetry in the depth of central and ventral portions of the central sulcus compared to males that produce less attention getting sounds with females showing the opposite pattern.…”

“…59 . Indeed, Hopkins et al 59 found that male chimpanzees producing attention getting sounds showed a larger leftward asymmetry in the depth of central and ventral portions of the central sulcus compared to males that produce less attention getting sounds with females showing the opposite pattern. We also recently showed that the presence of a PCGS and an intralimbic sulcus, particularly in the left hemisphere, was associated respectively with the production and use of attention-getting sounds by chimpanzees as well as rightward handedness (Hopkins et al, in preparation).…”

Reproducibility of leftward planum temporale asymmetries in two genetically isolated populations of chimpanzees ( Pan troglodytes )

“…The sequence of post-image processing steps performed on the images is shown in figure 1a-h and have been described in detail elsewhere [62][63][64]. The pipeline of processing used to extract the sulci from the raw T1-weighted image derives from a pipeline initially dedicated to the human brain and freely distributed as a BrainVISA (BV) toolbox (http://brainvisa.info) [65].…”

Orangutans show active voicing through a membranophone

“…It gives categorical support that fundamental voice control to produce new vowel-like and other new voiced calls is shared among humans and great apes 1 , even if the exact voice parameters/quality may have differed from extinct hominids depending on soft tissue anatomic differences in the vocal apparatus. Alongside a fast and ongoing multidisciplinary shift in our understanding of great ape vocal faculties 1,5–7 , this study demonstrates that behavioural prima materia for the evolution of articulate language was present among ancient members of the Homonidea family.…”