Join for Free!
111304 members
table of contents table of contents

Biology Articles » Evolutionary Biology » Human Evolution » What makes man human: thirty-ninth James Arthur lecture on the evolution of the human brain, 1970 » Brain function in awareness

Brain function in awareness
- What makes man human: thirty-ninth James Arthur lecture on the evolution of the human brain, 1970

"The experience of meaning is an experience of vital involvement. Not an experience of a private reference of meaning, but sharing a dimension open to all human beings."[1]

During the past decade a series of studies initiated by Kamiya has shown that people can discriminate their brain states [10]. These studies use electrical signals to indicate brain function and recordable behaviors as measures of psychological state. A subject readily acquires the ability to discriminate the occasions when his brain is giving off alpha rhythms from those when his brain's electrical activity is desynchronized. An interesting incidental finding in these studies has been the fact that when Zen and Yoga procedures accomplish their aims, subjects can attain the alpha brain rhythm state at will. Kamiya's training procedures can and are being used as a short cut to Nirvana.

More specific are some recent experiments of Libet that have explored a well-known phenomenon [11]. Since the demonstrations in the late 1800's by Fritsch and Hitzig that electrical stimulation of parts of man's brain results in movement [12], neurosurgeons have explored its entire surface to determine what reactions such stimulations will produce in their patients. For instance, Foerster mapped regions in the postcentral gyrus which give rise to awareness of one or another part of the body [13]. Thus sensations of tingling, of positioning, etc. can be produced in the absence of any observable changes in the body part experienced by the patient. Libet has shown that the awareness produced by stimulation is not immediate: a minimum of a half second and sometimes a period as long as five seconds elapses before the patient experiences anything. It appears that the electrical stimulation must set up some state in the brain tissue and only when that state has been attained does the patient experience.

What do we know about the organization of these brain states apparently so necessary to awareness? They display some curious properties. One would expect that when the brain rhythms which are correlated with the subject's report are disrupted, the behavioral functions would also be interfered with. This is not the case. Focal epileptic discharge in the postcentral gyrus and elsewhere, unless it becomes pervasive and takes over the function of a large part of the brain, does not seriously disrupt awareness [14]. I have densely scattered epileptic lesions in various areas of the nonhuman primate brain in a series of carefully carried out experiments and found that despite the electrical disturbance produced, problem-solving ability remains unimpaired provided the ability had been acquired before electrical seizure discharge began [15-17]. (The acquisition of appropriate performances after the discharges become established is, however, slowed approximately fivefold.)

In short, the brain state necessary to awareness appears to be resistant to being disrupted by local damage provided this damage is not overly extensive. An estimate of the limits on the extent to which disruption can take place without undue influence on the state comes from experiments involving brain tissue removals. Some 85 (or in some experiments even more) of a neural system can be made ineffective without seriously impairing the performances dependent on that system [18-20]. What sort of state is it that can function effectively when only 10 or 15 percent of it remains and all of what remains need not be concentrated in one location?

The answer is that the effective units of the state must be distributed across the tissue involved. Each unit or small cluster of units must be capable of performing in lieu of the whole. Until very recently it was difficult to conceive of such a mechanism.

But just as information processing by computer is an aid in conceptualizing the way in which coding operations are hierarchically constructed, so another engineering domain helps us to understand the problem of the "distributed" state. This domain is called optical information processing [21] because optical systems work this way; or, holography, because each part of a recorded state can stand in for the whole [22].

The essential characteristic of a holographic state is the encoding of the relation among recurrences of neighboring activities. This is known technically as a spatial phase relationship. In optics, ordinary pictures encode only the intensity of illumination at any location; a hologram encodes spatial phase in addition.

Holograms have many properties of interest to the brain scientist. Foremost of these is the fact that information is distributed in the holographic record. Thus one can take a small part of the hologram and reconstruct from it an image in most respects the same as that reconstructed from the whole record. Second, a great deal of information can be stored in one hologram. Several major companies (IBM, RCA) have been able to encode well over a million bits in a square centimeter. Third, an entire image can be reconstructed from a hologram when illumination is reflected from one feature or part of the scene originally recorded. This is the property of associative recall.

Holograms were first constructed mathematically by Dennis Gabor and crude reproductions were achieved [23,24]. Later they were improved immensely by illuminating the object with a laser beam (fig. 1). Because of the similarity of properties of the optical hologram and the facts about the brain reviewed in the passages above, I have suggested that one important encoding process in the brain follows the mathematical rules of holography [25]. My laboratory is now working on the problem of just how the hologram is realized in neural tissue [7].

The neural hologram is a state in which information is encoded in such a way that images can be constructed. Although images are evanescent, they occur. Although they cannot be directly communicated, they exist. At least three types of images can be discerned subjectively, however, and for each a separate neural system has been identified. Images constructed by the operations of the classical sensory systems refer to events external to the organism [25]; images constructed by the operations of the limbic forebrain monitor the world within [26,27]; and, images constructed by the brain's motor mechanisms structure the achievements an organism aims to accomplish [9, 28]. I want now to take a look at these motor mechanisms, for without them behavior could not occur and we could never make our images meaningful.

rating: 2.20 from 5 votes | updated on: 20 Jul 2007 | views: 7526 |

Rate article: