This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.
1998 Second Web Reports
Anosognosia is a disorder occurring in about 5% of patients who have had a stroke affecting the right side of their brain (6), in particular the right parietal cortex, causing left hemiplegia (paralysis of the side of the body opposite to the affected side of the brain). Its characteristic feature is the inability, or, some would say, unwillingness of patients to perceive their own paralysis, and in extreme cases, that of others. It is important to note that anosognosia occurs only when the right side of the brain is involved; the effects of damage to the left hemisphere are, as shall be explained later, quite different (1).
Dr. Vilayanur Ramachandran of UC San Diego has made anosognosia one of his primary foci of research and has proposed intriguing, neurological hypotheses as to what might be going on in anosognosiacs' brains. In his research, he has found that anosognosiacs do not deny paralysis merely because their brain damage causes them to be inattentive to the left side of their body; when attention is drawn to a paralyzed limb, by asking patients to perform simple motor tasks, for example, anosognosiacs will either assert that they are indeed carrying it out (when they obviously are not) (1,2,4,5,6) or make up stories to explain it away, claiming, for example, that their arthritis is acting up and that they therefore don't feel like doing it (1,2). In many cases, patients refuse to recognize the paralyzed limb as their own, accepting the bizarre and irrational implications such a statement brings with it (e.g., the limb belonging to a relative, their doctor having three arms) as quite normal (1).
As stated above, anosognosia affects only individuals with damage in the right parietal cortex of the brain; both cortices are responsible for "directing the brain's attention to movements, objects, and sensations on the opposite side of the body, as well as [perceiving] that entire side of the body in space," (1). It seems possible that forms of the disorder vary depending on which areas are damaged: for example, in Dr. Ramachandran's study of three 77-78 year-old women with anosognosia, he found that two of them denied both their own and another patient's paralysis, whereas the third denied only her own; the former had damage in the right middle cerebral artery and either the right or the left cerebellar artery, whereas the third patient (the one who perceived that the other patient was not moving his arm) had a right frontoparietal infarct (5). In other words, the first two women were affected both in their perception of themselves as well as others, whereas the site of damage in the third patient caused her to have warped perceptions only of herself. This issue of distorted perception of self as well as others will be discussed shortly, but I shall present explanations that have been proposed for the first type (i.e., that in which "only" the perception of the self is affected) before addressing the second.
Possible explanations in the past have been along two lines: they are either psychoanalytic/Freudian or neurological (1). In the first, the claim is that anosognosia is the ego's way of avoiding having to face the truth of a drastically altered self (1), a self-protective mechanism of the mind. Not only is this theory elusive, it also does not account for the fact that anosognosia occurs exclusively in patients with left hemiplegia and not in those whose left hemispheres have suffered damage (1,2,6). Neurological explanations have proposed a relationship between anosognosia and what is known as unilateral neglect, the failure of some stroke patients with damage in the right parietal cortex to pay attention to anything on the left side of their perceptive field, i.e., anosognosia is merely the result of an individual's neglect of the paralyzed left side of the body (1). However, as Dr. Ramachandran observed, it is possible for patients suffering from universal neglect to perceive objects on the neglected side if their attention is drawn to them; anosognosiacs, however, "do not passively ignore their paralysis; they actively deny it," (1).
Note that the word "deny" has been used to describe anosognosiacs behavior towards their paralysis, rather than "are unaware of" or "unable to perceive." Denial implies acknowledgment at some level, it cannot occur in a state of cognitive obliviousness. And indeed, according to Ramachandran, there is evidence of an awareness of paralysis at some level below that of consciousness: after having repeatedly failed at the required task (to tie a shoelace), one of his patients later told someone that she had indeed achieved it, "with both hands," as she made a point of saying (qtd. 1,2, emphasis added). Ramachandran proceeded to test his hypothesis using the findings of an experiment performed by Italian scientist Bisiach, which showed that pouring cold water into the left ear of anosognosiacs temporarily relieved their symptoms (for more info., see 1,6). When Ramachandran performed a similar experiment on one of his patients, he found that she readily admitted to her paralysis--until the effects of the water wore off, after which she not only lapsed back into denial of paralysis, but also of having ever admitted to it (1,2,6). It therefore seems probable that information about the "denied" side of the body, the information which is being denied, is nevertheless present in the brain; signals must be reaching it at some level but th"en be blocked before reaching the person's consciousness.
Ramachandran has formed a tentative explanation of his own to account for anosognosia, based on a hypothesis concerning the roles of the right and left hemispheres: recognizing that the brain is receiving "a bewildering variety of sensory inputs, all of which must be incorporated into a coherent perspective that's based on what stored memories already tell us is true about ourselves and the world," he speculates that there must be something in the nervous system which acts as a filter, something which selects from "this superabundance of detail and [orders] it into a consistent belief system," allowing one to carry out actions without becoming lost in indecision (Ramachandran, qtd. in 6). Since it is the right hemisphere which is damaged in anosognosia, he proposes that it is in the left hemisphere where such a belief system is created. To a certain degree, it culls out details from inputs which correspond to the already existing conception and ignores or adjusts (rationalizes) those which conflict with it, so that the overall "storyline" remains consistent (1,2,6). However, since it would be fatal to be entirely dismissive of conflicting inputs, there must be a mechanism whereby to override this tendency toward conformity should such "anomalous" input pass a certain threshold (1,2,6). Ramachandran believes that it is the right hemisphere which is responsible for detecting anomalies and forcing the left side "to revise the entire model" (qtd. in 6). In anosognosiacs, this "anomaly detector" (1) or "devil's advocate" (2) is impaired by the damage to various parts of the right hemisphere, and thus it cannot counterbalance what is going on on the other sidie of the brain. Ramachandran has also shown that anosognosiacs will deny sensory information (i.e., visual) about the activity and position of their healthy, right limbs when that information "has been intentionally brought into conflict," indicating that "perhaps, the functions damaged by the stroke involved more than the specific circuits concerned with the left side of the body," (1, see source for more details on experiment). Additional evidence for this last statement as well as for Ramachandran's theory about the "division of labor" (6) between the right and the left hemispheres, comes from his observations of the differences between patients with right-stroke damage and those with left-stroke damage in their attitudes and behavior towards emotionally upsetting news or information: those with damage to the right side of the brain (commonly associated with emotions, 1) "often appear oddly oblivious," while patients with left-brain damage tend to get wrapped up in or trapped by their emotions (1). According to Ramachandran's model, these differences can be accounted for in terms of either a damaged anomaly detector (right-brain damage) or an overly active one (left-brain damage) (1).
Having thus provided a viable hypothesis for distorted self-perception, one which is firmly grounded in the structure and functioning of the brain and which includes a wide range of applications, it can be extended to address the problem of anosognosia towards others' paralysis. The notion of a neural "map" of the body is a well-established concept in biology; if indeed there is an anomaly detector, and it is damaged, it would "[prevent] new sensory data from being integrated into the schema," producing anosognosia (4). Ramachandran and his colleagues have suggested the potential existence of a neural representation of others in addition to that of the self, close to, but not "completely [overlapping]" it (4). Evidence in support of this proposal comes from studies of monkeys, which have shown that there are "[c]ertain cells in the monkey frontal lobes [which] respond not only to their own hand performing certain actions but also to the visual image of another monkey's hand performing the same action" (5).
This model is intriguing not only because it may help to explain the curious effects of anosognosia, but also because of its implications for other topics of interest to scientists and human beings in general. The experiment described earlier, which was used to temporarily relieve the patient's anosognosia, also has the curious effect of producing the same kind of rapid eye movement seen in what is known as REM sleep, when we experience dreams (1). According to Ramachandran, REM sleep "'is [the] only...state in normal life where your eyes move back and forth and you pull up unpleasant memories and disturbing beliefs about yourself,'" (qtd. 1); perhaps this rapid eye movement signals increased activity of the anomaly detector in relation to the self-preservative filter in the left brain, linking the content of dreams to actual information received but not consciously perceived by the brain (1,6). In other words, perhaps the separation of dream and reality is no longer a useful distinction to make. If indeed there is a link between anosognosia and dreams, it would provide clues to long-standing questions: where do the contents of our dreams come from? are they fabrications of the mind, or, as Freud proposed, do they contain repressed information? how do they reflect each person's individual experience of reality?
An argument was made in the opening paragraph against psychological explanations for anosognosia, and I want to explain what caused this reaction: in an online lecture, Patrick Haggard of the Department of Psychology, UCL, describes anosognosia and a similar phenomenon, somatoparaphrenia ("delusional beliefs about the body," 3), as reactions of some inner Self, perhaps the I-function, to psychologically upsetting changes, such as paralysis. He says that the "failure to update the 'body schema' to reflect the paralyzed limb...seems to be due to a psychological unwillingness to accommodate the immobile limb within the body schema...to avoid having to accept the real deficit," (3). In his eyes, anosognosia "shows how important the ability to make voluntary movements is to a balanced sense of who we are: our personal identity," and he concludes by asking whether it is "so vital...that we will go 'mad' rather than forgo it," (3). To me, such statements are dangerously close to the 'magic' we have been warned against over and over again in class; they do not reflect the properties of neurons, but seem to imply the existence of an abstract ego which directs our behavior. Although one cannot entirely rule out this possibility, there is no way to test it scientifically--it can neither be proven nor falsified, and as such is not a productive line of inquiry for scientists to pursue. Ramachandran's hypothesis is particularly appealing because it "anchor[s] the airy abstractions of Freudian psychology in the physical flesh of the brain," (1), making it possible to conduct experiments whereby to test its validity. And, indeed, such experiments are already well underway, producing data which allow for revision and adjustments.
Perhaps my presentation of neurological and psychological approaches as binary opposites was a little extreme, for there are many similarities between the two; however, based on what I have learned in class so far, I have come to view any explanation which cannot be explained in terms of neurons and their properties with skepticism. I am finally realizing the extent to which abnormal brains can tell us something about so-called normal ones, and the work of Dr. Ramachandran has brought this point home more strongly than ever. As he put it, by studying individuals commonly seen as deviating from the norm, we "'realize [we're] really looking at T[ourselves], in amplified form,'" (qtd. 1).
1. "The Brain That Misplaced Its Body." (Discover Magazine)
2. "Denying the devil's advocate." (New Scientist)
3. "Lecture 8. Some selected aspects of motor cortex damage in man." (Patrick Haggard, Department of psychology, UCL)
4. "Mind Over Body." (Scientific American)
5. Blakeslee, Sandra. "Figuring Out the Brain From Its Acts of Denial." The New York Times, Tuesday, January 23, 1996.
6. Ramachandran, V.S. and Diane Rogers-Ramachandran. "Denial of disabilities in anosognosia." Nature, v382, August 8, 1996, p. 501.