In the proceeding section I described how conceptual (including both semantic and spatial) knowledge is stored in the brain. Many skills or special talents, however, are not based on stores of conceptual knowledge. As a child you might have learned to ride a bike. If I asked you how to ride a bike you might be able to tell me that to propel the bike forward, you push the pedals forward and downward alternating between your left and right foot. You might also be able to tell me that if you want to go left you turn the handlebars to the left and vice versa. The most difficult part of learning to ride a bike, however, is learning how to keep your balance, and although after several minutes you might be able to explain to me how you do this, when you ride a bike, even after decades of not having ridden one, you do not keep your balance by using stored conceptual knowledge. Rather you rely on what is called procedural memory.
There are many other examples of procedural memories that we use throughout our life, such as writing letters and typing. Many special talents used in sports and even the playing of musical instruments may be examples of procedural memories. Several experiments, performed in patients who have neurological disease, demonstrated that procedural memories are independent from both the episodic and semantic-conceptual forms of declarative memory. Episodic-declarative memories are important in knowing what, where, and when; for example, recalling when you dined out last week, what you had for dinner, and where you had dinner.
In a classical study, Corkin (1968) studied the episodic and procedural memory of the famous epilepsy patient H. M. This patient had severe seizures that could not be controlled with medications. Studies of his brain waves, the electroencephalogram (EEG), indicated that his seizures were coming from the anterior part of both temporal lobes. To help control these seizures, the neurosurgeons removed his right and left anterior temporal lobes.
The anterior temporal lobes contain several structures that are known to be important in the learning and recall of episodic memories, including a structure called the hippocampus and structures that are closely connected to the hippocampus such as the entorhinal and perirhinal cortex. Although removal of the patient's right and left anterior temporal lobe helped control his seizures, he was left with a profound episodic memory loss. Because this surgery did not alter his stores of conceptual knowledge (semantic memory), his intelligence remained the same, but he had lost the ability to make new episodic memories and hence could not recall when or where he had dinner or what he had for dinner on the prior evening.
To study his ability to form procedural memories, Corkin tested him using rotary pursuit apparatus. This machine has a turntable that rotates like one of the old phonograph turntables. On one side of the turntable there is a small circular disk. The participant is given a metal wand and asked to keep the tip of this metal wand on this metal disk while it is rotating. Each day when H. M. was brought to the laboratory, he did not recognize the investigators performing this experiment and had to be reintroduced. He also did not recall the instructions for using the rotary pursuit apparatus and hence had to be given the instructions each day he was tested. Although he could not recall the laboratory staff or the instructions to use this apparatus, he showed that he could learn this procedure, improving his performance each day and thereby demonstrating that procedural memories or are different from episodic-declarative memories. Other investigators have studied the ability of other people who had severe amnesia (an inability to form new episodic memories) to form new conceptual-semantic memories. New words are always being introduced into our vocabulary (e.g., Internet), and in these studies the investigators knew the approximate date when these people developed amnesia and attempted to see if these people had learned new words that had been invented after the onset of their amnesia. They found that these people did learn new words after they suffered a permanent amnesia and hence were able to form new semantic-conceptual memories. One study even examined two people who were born with damage to the structures important for forming episodic memories and found that they had the normal development of semantic-conceptual memories and even performed well on IQ tests (Vargha-Khadem et al., 1997).
Further support for the postulate that the development of procedural memories can be dissociated from episodic and semantic-conceptual memories comes from a study performed in our laboratory. We studied patients with Alzheimer's disease, which affects both episodic and semantic-conceptual memories, by using a rotary pursuit motor-learning paradigm similar to that used by Corkin with H. M., the patient who had both anterior temporal lobes removed. Patients with Alzheimer's disease have amnesia because they have damage to the neurons in the medial temporal lobe (the same area that was surgically removed in H. M.), and they have problems with their semantic-conceptual memories because the neurons in the polymodal cortex are also damaged. When we examined these patients' ability to learn a new motor skill, however, they did as well as matched controls (Jacobs et al., 1999). These results provide further evidence that procedural memory is not mediated by the medial temporal lobe or polymodal-supramodal cerebral cortex.
Deep in each cerebral hemisphere there are clusters of neurons. One of these clusters is called the basal ganglia and the other is called the thalamus (see Figure 3.10). After decades of research that has attempted to determine the function of these basal ganglia, their function is still not entirely clear. One of the diseases, however, that affects these basal ganglia is Parkinson's disease. Normal basal ganglia function is dependent on the neurotransmitter dopamine, and in Parkinson's disease there is insufficient dopamine. Procedural memory was assessed in patients with Parkinson's disease by having them repeatedly use the rotary pursuit apparatus. Unlike H. M., the patients with amnesia from removal of the temporal lobes, and the patients with Alzheimer's disease, the subjects with Parkinson's disease were impaired at improving their skills, indicating a procedural memory deficit. These participants with Parkinson's disease, however, had normal episodic memories and semantic-conceptual knowledge. Thus, it appears that these basal ganglia are important for developing procedural memories. Exactly how they encode procedural memories is unknown, but these basal ganglia appear to be part of a neuronal loop that starts in the cortex (primarily in the frontal lobes), proceeds to the putamen, then to the global pallidus, then to the thalamus, and back to the cortex (Figure 3.10). Different parts of the cortex appear to project to different parts of the basal ganglia, and, although it is not thoroughly investigated, different loops might be important for mediating different forms of procedural memories. Many talented people—including athletes, singers, dancers, musicians, and even artists—depend heavily on these procedural memories.
Unlike episodic or semantic-conceptual memories, which can be learned after one exposure to stimuli, procedural memories require
practice and feedback. For some reason, procedural memories are best acquired in childhood; thus, the best time to teach skilled behaviors, from learning the violin to playing golf, is in childhood. Most famous golfers like Tiger Woods or tennis players like Pete Sampras started to learn to play their sports when they were children. Most famous musicians also learned to play their instruments in childhood. The reason adults are slower to learn procedural memories is not known, but it might relate to a decrease in the neurotransmitter dopamine that occurs with aging.
Although almost all people who excel in productive arts—such as musicians, singers, and painters—have extraordinary procedural memories in the domain of their talent, there is not a direct relationship between productive talent and creativity. Although many talented musicians might interpret the music they are playing, most performers are playing the music that someone else composed and have not successfully composed their own creative pieces. Similarly, actors interpret the lines written by the playwright, but although interpretation is a form of creativity, it is only a minor form. Thus, although procedural memories are important in the performance or production of creative works, there is little evidence that they are important in creative innovation. In addition, I could not find any studies that demonstrate differences between the brains of extremely talented people and those without special talents. Earlier I mentioned that there are also no studies of the cerebral cortex or white matter connections in extremely creative people. Thus, overall there is no strong evidence for a structural-anatomic basis of genius, but I also think that structural-anatomic hypotheses have not been adequately investigated.
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