SUPERIOR PARIETAL LOBULE (SPL) A brain region that lies near the top of the parietal lobe. The right SPL is partially concerned with creating one’s body image using inputs from vision and area S2 (joint and muscle sense). The inferior parietal lobule is also involved in this function.
SUPERIOR TEMPORAL SULCUS (STS) The topmost of two horizontal furrows, or sulci, in the temporal lobes. The STS has cells that respond to changing facial expressions, biological movements such as gait, and other biologically salient inputs. The STS sends its output to the amygdala.
SUPRAMARGINAL GYRUS An evolutionarily recent gyrus that split off from the inferior parietal lobule. The supramarginal gyrus is involved in the contemplation and execution of skilled or semiskilled movements. It is unique to humans, and damage to it leads to apraxia.
SYMPATHETIC NERVOUS SYSTEM A branch of the autonomic nervous system, responsible for mobilizing the body’s energy and resources during times of stress and arousal. It does this by regulating temperature as well as increasing blood pressure, heart rate, and sweating in anticipation of exertion.
SYNAPSE A gap between two neurons that functions as the site of information transfer from one neuron to another.
SYNESTHESIA A condition in which a person literally perceives something in a sense besides the sense being stimulated, such as tasting shapes or seeing colors in sounds or numbers. Synesthesia is not just a way of describing experiences as a writer might use metaphors; some synesthetes actually experience the sensations.
SYNTAX Word order that enables compact representation of complex meaning for communicative intent; loosely synonymous with grammar. In the sentence “The man who hit John went to the car,” we recognize instantly that “the man” went to the car, not John. Without syntax we could not arrive at this conclusion.
TEMPORAL LOBE One of the four major subdivisions (the others being frontal, parietal, and occipital lobes) of each cerebral hemisphere. The temporal lobe functions in perception of sounds, comprehension of language, visual perception of faces and objects, acquisition of new memories, and emotional feelings and behavior.
TEMPORAL LOBE EPILEPSY (TLE) Seizures confined mainly to the temporal lobes and sometimes the anterior cingulate. TLE may produce a heightened sense of self and has been linked to religious or spiritual experiences. The person may undergo striking personality changes and/or become obsessed with abstract thoughts. People with TLE have a tendency to ascribe deep significance to everything around them, including themselves. One explanation is that repeated seizures may strengthen the connections between two areas of the brain: the temporal cortex and the amygdala. Interestingly, people with TLE tend to be humorless, a characteristic also seen in seizure-free religious people.
THALAMUS A structure consisting of two egg-shaped masses of nerve tissue, each about the size of a walnut, deep within the brain. The thalamus is the key “relay station” for sensory information, transmitting and amplifying only information of particular importance from the mass of signals entering the brain.
THEORY OF MIND The idea that humans and some higher primates can construct a model in their brains of the thoughts and intentions of other people. The more accurate the model, the more accurately and rapidly the person can predict the other person’s thoughts, beliefs, and actions. The idea is that there are specialized brain circuits in human (and some apes’) brains that allow for theory of mind. Uta Frith and Simon Baron-Cohen have suggested that autistic children may have a deficient theory of mind, which complements our view that a dysfunction of mirror neurons or their targets may underlie autism.
WERNICKE’S AREA A brain region responsible for the comprehension of language and the production of meaningful speech and writing.
“WHAT” STREAM The temporal lobe pathway concerned with recognizing objects and their meaning and significance. Also called pathway 2. See also new pathway and “how” stream.
NOTES
PREFACE
1. I have since learned that this observation has resurfaced from time to time, but for obscure reasons isn’t part of mainstream oncology research. See, for example, Havas (1990), Kolmel et al. (1991), or Tang et al. (1991).
INTRODUCTION: NO MERE APE
1. This basic method for studying the brain is how the whole field of behavioral neurology got started back in the nineteenth century. The major difference between then and now is that in those days there was no brain imaging. The doctor had to wait around for a decade or three for the patient to die, then dissect his brain.
2. In contrast to the hobbits, African pigmies, who are also extraordinarily short, are modern humans in every way, from their DNA right on up through their brains, which are the same size as those of all other human groups.
CHAPTER 2 SEEING AND KNOWING
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.