Read Phantoms in the Brain: Probing the Mysteries of the Human Mind for Free Online Page B
Authors: V. S. Ramachandran, Sandra Blakeslee
fellow, it turns out, had a tiny stroke that only 16
affected his basal ganglia selectively on one side of the brain.
Yawning provides further proof for specialized circuitry. As noted, many stroke victims are paralyzed on the right or left side of their bodies, depending on where the brain injury occurs. Voluntary movements on the opposite side are permanently gone. And yet when such a patient yawns, he stretches out both arms spontaneously. Much to his amazement, his paralyzed arm suddenly springs to life! It does so because a different brain pathway controls the arm movement during the yawn— a pathway closely linked to the respiratory centers in the brain stem.
Sometimes a tiny brain lesion—damage to a mere speck of cells among billions—can produce far−reaching problems that seem grossly out of proportion to the size of the injury. For example, you may think that memory involves the entire brain. When I say the word "rose," it evokes all sorts of associations: perhaps images of a rose garden, the first time someone ever gave you a rose, the smell, the softness of petals, a person named Rose and so on. Even the simple concept of "rose" has many rich associations, suggesting that the whole brain must surely be involved in laying down every memory trace.
But the unfortunate story of a patient known as H.M. suggests otherwise.9 Because H.M. suffered from a particularly intractable form of epilepsy, his doctors decided to remove "sick" tissue from both sides of his brain, including two tiny seahorse−shaped structures (one on each side) called the hippocampus, a structure that controls the laying down of new memories. We only know this because after the surgery, H.M. could no longer form new memories, yet he could recall everything that happened before the operation. Doctors now treat the hippocampus with greater respect and would never knowingly remove it from both sides of the brain (Figure 1.3).
Although I have never worked directly with H.M., I have often seen patients with similar forms of amnesia resulting from chronic alcoholism or hypoxia (oxygen starvation in the brain following surgery). Talking to them is an uncanny experience. For example, when I greet the patient, he seems intelligent and articulate, talks normally and may even discuss philosophy with me. If I ask him to add or subtract, he can do so without trouble. He's not emotionally or psychologically disturbed and can discuss his family and their various activities with ease.
Then I excuse myself to go to the restroom. When I come back, there is not a glimmer of recognition, no hint that he's ever seen me before in his life.
"Do you remember who I am?"
"No."
I show him a pen. "What is this?"
"A fountain pen."
"What color is it?"
"It's red."
I put the pen under a pillow on a nearby chair and ask him, "What did I just do?"
He answers promptly, "You put the pen under that pillow."
17
Then I chat some more, perhaps asking about his family. One minute goes by and I ask, "I just showed you something. Do you remember what it was?"
He looks puzzled. "No."
Figure 1.3 Artist's rendering of a brain with the outer convoluted cortex rendered partially transparent to allow inner structures to be seen. The thalamus (dark) can be seen in the middle, and interposed between it and the cortex are clusters of cells called the basal ganglia (not shown). Embedded in the front part of the temporal lobe you can see the dark, almond−shaped amygdala, the "gateway" to the limbic system. In the temporal lobe you can also see the hippocampus (concerned with memory). In addition to the amygdala, other parts of the limbic system such as the hypothalamus (below the thalamus) can be seen. The limbic pathways mediate emotional arousal. The hemispheres are attached to the spinal cord by the brain stem (consisting of medulla, pons and midbrain), and below the occipital lobes is the cerebellum, concerned mainly with coordination of movements and timing. From Brain,
affected his basal ganglia selectively on one side of the brain.
Yawning provides further proof for specialized circuitry. As noted, many stroke victims are paralyzed on the right or left side of their bodies, depending on where the brain injury occurs. Voluntary movements on the opposite side are permanently gone. And yet when such a patient yawns, he stretches out both arms spontaneously. Much to his amazement, his paralyzed arm suddenly springs to life! It does so because a different brain pathway controls the arm movement during the yawn— a pathway closely linked to the respiratory centers in the brain stem.
Sometimes a tiny brain lesion—damage to a mere speck of cells among billions—can produce far−reaching problems that seem grossly out of proportion to the size of the injury. For example, you may think that memory involves the entire brain. When I say the word "rose," it evokes all sorts of associations: perhaps images of a rose garden, the first time someone ever gave you a rose, the smell, the softness of petals, a person named Rose and so on. Even the simple concept of "rose" has many rich associations, suggesting that the whole brain must surely be involved in laying down every memory trace.
But the unfortunate story of a patient known as H.M. suggests otherwise.9 Because H.M. suffered from a particularly intractable form of epilepsy, his doctors decided to remove "sick" tissue from both sides of his brain, including two tiny seahorse−shaped structures (one on each side) called the hippocampus, a structure that controls the laying down of new memories. We only know this because after the surgery, H.M. could no longer form new memories, yet he could recall everything that happened before the operation. Doctors now treat the hippocampus with greater respect and would never knowingly remove it from both sides of the brain (Figure 1.3).
Although I have never worked directly with H.M., I have often seen patients with similar forms of amnesia resulting from chronic alcoholism or hypoxia (oxygen starvation in the brain following surgery). Talking to them is an uncanny experience. For example, when I greet the patient, he seems intelligent and articulate, talks normally and may even discuss philosophy with me. If I ask him to add or subtract, he can do so without trouble. He's not emotionally or psychologically disturbed and can discuss his family and their various activities with ease.
Then I excuse myself to go to the restroom. When I come back, there is not a glimmer of recognition, no hint that he's ever seen me before in his life.
"Do you remember who I am?"
"No."
I show him a pen. "What is this?"
"A fountain pen."
"What color is it?"
"It's red."
I put the pen under a pillow on a nearby chair and ask him, "What did I just do?"
He answers promptly, "You put the pen under that pillow."
17
Then I chat some more, perhaps asking about his family. One minute goes by and I ask, "I just showed you something. Do you remember what it was?"
He looks puzzled. "No."
Figure 1.3 Artist's rendering of a brain with the outer convoluted cortex rendered partially transparent to allow inner structures to be seen. The thalamus (dark) can be seen in the middle, and interposed between it and the cortex are clusters of cells called the basal ganglia (not shown). Embedded in the front part of the temporal lobe you can see the dark, almond−shaped amygdala, the "gateway" to the limbic system. In the temporal lobe you can also see the hippocampus (concerned with memory). In addition to the amygdala, other parts of the limbic system such as the hypothalamus (below the thalamus) can be seen. The limbic pathways mediate emotional arousal. The hemispheres are attached to the spinal cord by the brain stem (consisting of medulla, pons and midbrain), and below the occipital lobes is the cerebellum, concerned mainly with coordination of movements and timing. From Brain,
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