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

1. Strictly speaking, the fact that octopuses and humans both have complex eyes is probably not an example of true convergent evolution (unlike the wings of birds, bats, and pterosaurs). The same master control genes are at work in “primitive” eyes as in our own. Evolution sometimes reuses genes that have been stored away in the attic.

2. John was originally studied by Glyn Humphreys and Jane Riddoch, who wrote a beautiful monograph about him: To See but Not to See: A Case Study of Visual Agnosia (Humphreys & Riddoch, 1998). What follows is not a literal transcript but for the most part preserves the patient’s original comments. John suffered from an embolus following appendectomy as indicated, but the circumstances leading up to the appendectomy are a reenactment of the way things might have occurred during a routine diagnosis of appendicitis. (As mentioned in the Preface, to preserve patient confidentiality, throughout the book I often use fictitious names for patients and alter circumstances of hospital admission that are not relevant to the neurological symptoms.)

3. Can you see the Dalmatian dog in Figure 2.7?

4. The distinction between the “how” and “what” pathways is based on the pioneering work of Leslie Ungerleider and Mortimer Mishkin working at the National Institutes of Health. Pathways 1 and 2 (“how” and “what”) are clearly defined anatomically. Pathway 3 (dubbed “so what,” or the emotional pathway) is currently considered a functional pathway, as inferred from physiological and brain lesion studies (such as studies on the double dissociation between the Capgras delusion and prosopagnosia; see Chapter 9).

5. Joe LeDoux has discovered there is also a small, ultra-shortcut pathway from the thalamus (and possibly the fusiform gyrus) directly to the amygdala in rats, and quite possibly in primates. But we won’t concern ourselves with that here. The details of neuroanatomy are unfortunately far messier than we would like, but that shouldn’t stop us from looking for overall patterns of functional connectedness, as we’ve been doing.

6. This idea about the Capgras syndrome was proposed independently of us by Hadyn Ellis and Andrew Young. However, they postulate a preserved “how” stream (pathway 1) and combined damage to the two components of the “what” stream (pathways 2 plus 3), whereas we postulate a selective damage to the emotional stream (pathway 3) alone with sparing of pathway 2.

CHAPTER 3 LOUD COLORS AND HOT BABES: SYNESTHESIA

1. Several experiments point to the same conclusion. In our very first paper on synesthesia, published in 2001 in the Proceedings of the Royal Society of London, Ed Hubbard and I noted that in some synesthetes the strength of color induced seemed to depend not just on the number but on where in the visual field it was presented (Ramachandran & Hubbard, 2001a). When the subject looked straight, then numbers or letters presented off to one side (but made larger to be equally visible) seemed less vividly colored than ones presented in central vision. This, in spite of the fact that they were equally identifiable as particular numbers and in spite of the fact that real colors are just as vividly visible in off-axis (peripheral) vision. Again, these results exclude high-level memory associations as the source of synesthesia. Visual memories are spatially invariant. By that I mean that when you learn something in one region of your visual field—recognizing a particular face, for instance—you can recognize the face presented in a completely new visual location. The fact that the evoked colors are different in different regions argues strongly against memory associations. (I should add that even for the same eccentricity the color is sometimes different for left and right halves of the visual field; possibly because the cross-activation is more pronounced in one hemisphere than the other.)

2. This basic result—that the 2s are more quickly segregated from the 5s in synesthetes than in nonsynesthetes—has been confirmed by other scientists, especially Randolph Blake and Jamie Ward. In a meticulously controlled experiment, Ward and his colleagues found that synesthetes as a group are significantly better than control subjects at seeing the embedded shape made of 2s. Intriguingly, some of them perceived the shape even before any color was evoked! This lends credibility to our early cross-activation model; it’s possible that during brief presentations the colors are evoked sufficiently strongly to permit segregation to occur but not strongly enough to evoke consciously perceived colors.