Self Comes to Mind

by certain strokes, tumors, and late-stage Alzheimer’s disease. In coma and vegetative states the compromise is radical, akin to a sledgehammer applied pointedly and unkindly to a brain territory.
    Alzheimer’s Disease . Alzheimer’s, a uniquely human disease, is also one of the most serious health problems of modern times. As we attempt to understand it, however, and on a rather positive note, the condition has also become a source of valuable information about mind, behavior, and brain. The contributions of Alzheimer’s disease to the understanding of consciousness are only now becoming apparent.
    Beginning in the 1970s, I had the opportunity of following many patients with this condition and the privilege of studying their brains at postmortem, both the gross specimen and the microscopic material. In those years part of our research program was devoted to Alzheimer’s disease, and my colleague and close collaborator Gary W. Van Hoesen was a leading expert in the neuroanatomy of the Alzheimer’s brain. Our main goal then was understanding how circuit changes in the Alzheimer’s brain could cause the disturbance of memory that characterized the condition.
    Most patients with typical Alzheimer’s disease do not have disturbances of consciousness, either early in the disease or in its midstages. The first years of the disease are hallmarked by progressive defects in learning new factual information and in recalling previously learned factual information. Difficulties with judgment and spatial navigation are also common. Early on the touch of the disease may be so light that social graces are preserved and some semblance of life normality does persist for a while.
    In the early 1980s our research group, which by then included Brad Hyman, established a reasonable cause for the factual memory defect in Alzheimer’s disease: the extensive neuropathological changes in the entorhinal cortex and in the adjoining fields of the anterior temporal lobe cortices. 11 The hippocampus, the brain structure needed to lock in new memories of facts elsewhere in the brain, was effectively disconnected from the entorhinal/anterior temporal lobe cortices. As a consequence, new facts could not be learned. In addition, as the disease progressed, the anterior temporal lobe cortices were themselves so damaged that they prevented access to unique, previously learned factual information. In effect, the bedrock of autobiographical memory was eroded and was eventually just as wiped out as in patients with massive destruction of the temporal lobe caused by herpes simplex enceph alitis, a viral infection whose brunt also compromises the anterior temporal regions selectively. The cellular specificity of Alzheimer’s disease was uncanny. Most if not all neurons of layers II and IV of the entorhinal cortex were turned into tombstones, the best description for what is left of neurons after the disease changes them into neurofibrillary tangles. What this selective insult accomplished was a razor-sharp cut in the input lines to the hippocampus, which use layer II as a relay. And in order to make the severance complete, the insult also made an equally sharp cut in output lines from the hippocampus, those that use layer IV. Little wonder that factual memory is devastated in Alzheimer’s.
    As the disease progresses, however, along with other selective disturbances of mind, the integrity of consciousness begins to suffer. At first, the problem is predictably confined to autobiographical consciousness. Because memory about past personal events cannot be properly retrieved, the link between current events and the lived past becomes inefficient. Reflective consciousness in deliberative, offline processing is compromised. In all likelihood, part of this disturbance, though perhaps not all, is still due to medial temporal lobe dysfunction.
    Further along its inexorable march, the ravage extends well beyond autobiographical processes. In the late stages of Alzheimer’s, in those patients who receive good medical and nursing care and who survive the longest, a virtually vegetative state gradually sets in. The patients’ connection to the world is reduced to a point where they resemble individuals in akinetic mutism. The patients initiate fewer and fewer interactions with the physical and human surroundings and respond to fewer and fewer prompts. Their emotions are muted. Their behavior is dominated by an absent, listless, vacant, unfocused, silent