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

The posterior insula then relays to the front (anterior) part of the insula. The eminent neuroanatomist, Arthur D. (Bud) Craig, from the Barrow Neurological Institute in Phoenix, has suggested that the posterior insula registers only rudimentary unconscious sensations, which need to be “re-represented” in more sophisticated form in the anterior insula before your body image can be consciously experienced.

Craig’s “re-representations” are loosely similar to what I called “metarepresentations” in Phantoms in the Brain. But in my scheme, further back-and-forth interactions with the anterior cingulate and other frontal structures are required for constructing your full sense of being a person reflecting on your sensations and making choices. Without these interactions it makes little sense to speak of a conscious self, whether embodied or not.

So far in this book, I have said very little about the frontal lobes, which became especially well developed in hominins and must play an important role in our uniqueness. Technically the frontal lobes are comprised of the motor cortex as well as the bulk of the cortex in front of it—the prefrontal cortex. Each prefrontal lobe has three subdivisions: the ventromedial prefrontal (VMF), or bottom inner part; the dorsolateral (DLF), or upper outer part; and the dorsomedial (DMF), or upper inner part (see Figure Int.2, in the Introduction). (Because the colloquial term “frontal lobes” includes the prefrontal cortex as well, I use “F” in these abbreviations, not “P.”) Let’s consider some of the functions of these three prefrontal regions.

I invoked the VMF in Chapter 8 when discussing pleasurable aesthetic responses to beauty. The VMF also receives signals from the anterior insula to generate your conscious sense of being embodied. In conjunction with parts of the anterior cingulate cortex (ACC), it motivates “desire” to take action. For instance, the discrepancy in body image in apotemnophilia, picked up in the right anterior insula, would be relayed to the VMF and the anterior cingulate to motivate a conscious plan of action: “Go to Mexico and get the arm removed!” In parallel, the insula projects directly to the amygdala, which activates the autonomic fight-or-flight response via the hypothalamus. That would explain the heightened skin sweating (galvanic skin response, or GSR) that we saw in our patients with apotemnophilia.

Of course, all this is pure speculation; at this point we don’t even know whether my explanation of apotemnophilia is correct. Nonetheless, my hypothesis illustrates the style of reasoning needed to explain many brain disorders. Just brushing such disorders aside as being “mental” or “psychological” problems serves no purpose; such labeling neither illuminates normal function nor helps the patient.

Given their extensive connections with limbic structures, it is hardly surprising that the medial frontal lobes—the VMF and possibly the DMF—are also involved in setting up the hierarchy of values that govern your ethics and morality, traits that are especially well developed in humans. Unless you are a sociopath (who has disturbances in these circuits, as shown by Antonio Damasio), you don’t usually lie or cheat, even when 100 percent sure you could get away with it if you tried. Indeed, your sense of morality and your concern for what others think of you are so powerful that you even act to extend them beyond your death. Imagine you have been diagnosed with terminal cancer and have old letters in your drawers that could be dredged up after your death, incriminating you in a sex scandal. If you are like most people, you will promptly destroy the evidence, even though logically, why should your posthumous reputation matter to you once you are gone?

I have already hinted at the role of mirror neurons in empathy. Apes almost certainly have empathy of sorts, but humans have both empathy and “free will,” the two necessary ingredients for moral choice. This trait requires a more sophisticated deployment of mirror neurons—acting in conjunction with the anterior cingulate—than any ape before us has achieved.

Let’s turn now to the dorsomedial prefrontal area (DMF). The DMF has been found in brain-imaging studies to be involved in conceptual aspects of the self. If you are asked to describe your own attributes and personality traits (rather than someone else’s), this area lights up in brain-imaging studies. On the other hand, if you were to describe the raw feel of your embodiment, one would expect your VMF to light up, but this hasn’t been tested yet.