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

FIGURE 9.1 A highly schematic diagram of the visual pathways and other areas invoked to explain symptoms of mental illness: The superior temporal sulcus (STS) and supramarginal gyrus (SM) are probably rich in mirror neurons. Pathways 1 (“how”) and 2 (“what”) are identified anatomical pathways. The split of the “what” pathway into two streams—“what” (pathway 2) and “so what” (pathway 3)—is based mainly on functional considerations and neurology. The superior parietal lobule (SPL) is involved in the construction of body image and visual space. The inferior parietal lobule (IPL) is also concerned with body image, but also with prehension in monkeys and (probably) apes. The supramarginal gyrus (SM) is unique to humans. During hominin development, it split off from the IPL and became specialized for skilled and semiskilled movements such as tool use. Selection pressure for its split and specialization came from the need to use hands for making tools, wielding weapons, hurling missiles, as well as fine hand and finger manipulation. Another gyrus (AG) is probably unique to us. It split off from IPL and originally subserved cross-modal abstraction capacities, such as tree climbing, and matching visual size and orientation with muscle and joint feedback. The AG became exapted for more complex forms of abstraction in humans: reading, writing, lexicon, and arithmetic. Wernicke’s area (W) deals with language (semantics). The STS also has connections with the insula (not shown). The amygdaloid complex (A, including the amygdala) deals with emotions. The lateral geniculate nucleus (LGN) of the thalamus relays information from the retina to area 17 (also known as V1, the primary visual cortex). The superior colliculus (SC) receives and processes signals from the retina that are to be sent via the old pathway to the SPL (after a relay via the pulvinar, not shown). The fusiform gyrus (F) is involved in face and object recognition.

FIGURE 9.2 An abbreviated version of Figure 9.1, showing the distinction between emotions and semantics (meaning).

SELF DUPLICATION: DOCTOR, WHERE IS THE OTHER DAVID?