The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human

FIGURE 6.2 A schematic depiction of resonance between brain areas that may have accelerated the evolution of protolanguage. Abbreviations: B, Broca’s area (for speech and syntactic structure). A, auditory cortex (hearing). W, Wernicke’s area for language comprehension (semantics). AG, angular gyrus for cross-modal abstraction. H, hand area of the motor cortex, which sends motor commands to the hand (compare with Penfield’s sensory cortical map in Figure 1.2). F, face area of the motor cortex (which sends command messages to the facial muscles, including lips and tongue). IT, the inferotemporal cortex/fusiform area, which represents visual shapes. Arrows depict two-way interactions that may have emerged in human evolution: 1, connections between the fusiform area (visual processing) and auditory cortex mediate the bouba-kiki effect. The cross-modal abstraction required for this probably requires initial passage through the angular gyrus. 2, interactions between the posterior language areas (including Wernicke’s area) and motor areas in or near Broca’s area. These connections (the arcuate fasciculus) are involved in cross-domain mapping between sound contours and motor maps (mediated partly by neurons with mirror-neuron-like properties) in Broca’s area. 3, cortical motor-to-motor mappings (synkinesia) caused by links between hand gestures and tongue, lip, and mouth movements in Penfield’s motor map. For example, the oral gestures for “diminutive,” “little,” “teeny-weeny,” and the French phrase “en peau” synkinetically mimic the small pincer gesture made by opposing thumb and index finger (as opposed to “large” or “enormous”). Similarly, pouting your lips outward to say “you” or (in French) “vous” mimic pointing outward.

There was an accelerated development of the left IPL in primate evolution culminating in humans. In addition, the front part of the lobule in humans (and humans alone), split into two gyri called the supramarginal gyrus and the angular gyrus. It doesn’t require deep insight to suggest therefore that the IPL and its subsequent splitting must have played a pivotal role in the emergence of functions unique to humans. Those functions, I suggest, include high-level types of abstraction.

The IPL (including the angular gyrus)—strategically located between the touch, vision, and hearing parts of the brain—evolved originally for cross-modal abstraction. But once this happened, cross-modal abstraction served as an exaptation for more high-level abstraction of the kind we humans take great pride in. And since we have two angular gyri (one in each hemisphere), they may have evolved different styles of abstraction: the right for visuospatial and body-based metaphors and abstraction, and the left for more language-based metaphors, including puns. This evolutionary framework may give neuroscience a distinct advantage over classical cognitive psychology and linguistics because it allows us to embark on a whole new program of research on the representation of language and thought in the brain.