The Time-Memory Complex

PERSPECTIVES IN BIOLOGY AND MEDICINE Volume 31 ¦ Number 3 ¦ Spring 1988 THE TIME-MEMORY COMPLEX RAGNAR GRANIT* Largely owing to the relativity theory, time as a physical concept has played an exciting role in the last half of this century. Less interest has been devoted to time in a biological context. Obviously, time is also a physical reality in the physiological experiment, say, in tracing the activity of a reflex pathway or in following the course of a chemical reaction. This may be called time as "hardware." But in these comments I am dealing with time manifesting itself in consciousness and intend to refer to it as "software." In this capacity, time has important creative functions , best known from the sensory domain. A good example is the vivid percept of velocity in vision. In acoustics, the whole tonal world is a temporal integration. As software, time is at the disposal of the organism for the creation of novelty. Its major adjuvant in this task is memory. By definition memory is something that unfolds in a temporal dimension. One major property of memory is its duration. Neglect time by giving it zero value, and memory is gone. It is this connection between time and memory that the term time-memory complex is meant to emphasize. In the physiological experiment, durability of a state of excitation or inhibition is assumed to be the basis of memory regarded as measurable hardware. This may well be true and as close to the physiology of remembering as we are likely to arrive. But the time-memory complex as it expresses itself in a software sequence contains more than the time course of a long-lasting measurable synaptic event. As a first example, This paper was read on the occasion of the 250th Anniversary of the founding of the Georg August University, in Göttingen, Germany, May 26, 1987. ?Address: Eriksbergsgatan 14, 11430 Stockholm, Sweden.© 1988 by The University of Chicago. All rights reserved. 0031-5982/88/3103-0582$01.00 Perspectives in Biology and Medicine, 31,3 ¦ Spring 1988 \ 313 consider the process of feature detection by a cell within the cortical projection of some sensory afférents. This concept itself is a hybrid between a software notion of a "feature" as perceived by a mind and a hardware experimental finding whose relevance is legitimized by the electrical response of a cell to which the feature is presented. The cell chooses between yes or no. In the background is the general idea of localization in the brain of software specifications. There is, of course, a pure hardware notion of localization as, for instance, in the hunt for the site of the nucleus of the vagus nerve. However, the more interesting development in this context has concerned software-hardware relations as initiated in the 1860s by Broca's discovery of the speech motor center. Recording from single cortical cells has added an element of analytical precision to this field of study. If this development is considered from the point of view of formation of time-memory complexes, recording from a single cortical cell is merely the last memorized part of something begun in the periphery. Consider, for instance, the well-known Hubel and Wiesel discovery of visual cells in the striate area sensitive to the orientation of an object presented on a vertical screen that the animal is viewing. The timememory complex has its roots in the receptive fields organized by the retinal center, it undergoes evaluation and transformation at the level of the geniculate body, and it is finally reorganized in the striate area where it is recorded. The directional sensitivity of the striate cell is thus the end result of an extended process of "editing" fixed by a sequential timememory complex to its purposive end. In a wider sense, localization refers to this extensive structure and not merely to the final site at which the feature is being recorded. The timed subconscious memory is always likely to occupy more space and time than what reaches awareness. Time-memory complex as a concept covers both conscious and subconscious components of the whole sequence. Sequential processes combining time and memory are the basis of everything we...