The Use of the Fish in Neuropsychology

THE USE OF THE FISH IN NEUROPSYCHOLOGY DAVID J. INGLE* . . . and there is a long, long road to travel before we shall be able to understand in any but the most shadowy outlines what a fish's mind is really like.—C. J. Herrick [i] I. Introduction This essay aims to commend the teleost fish as an experimental animal to neuropsychologists. Such persuasion would have seemed superfluous to neuroanatomists and psychologists ofone or two generations ago, who found among the fishes fascinating subjects for description and experiment . In the spirit of phylogenetic comparison, many workers believed that the progressive sprouting of neocortex along the vertebrate series was intimately bound up with the evolution ofintelligence. This outlook focused attention upon the uncorticated fish as a "creature of instinct." Later studies offish behavior revealed unsuspected capacities for learning [2, 3] which compare favorably with those ofsome mammals. Despite increasing appreciation of the evolutionary process, major studies in neuropsychology are today restricted to the mammals almost exclusively. Because the hope is to understand the brain and behavior of man, this is understandable. However, fundamental notions regarding brain function will necessarily be general concepts, and we ought not constrain our imagination by our familiarity with the architecture ofthe mammalian brain. In the search for underlying mechanisms, the comparative method is useful. But ifthe anatomical substrate offish behavior differs from the brains ofcat and monkey while behavioral functions are similar, we should be cautious about simple correlations between structure and function. Study ofhigher mental faculties—perception, memory, and intelligence •Department ofPsychology, Massachusetts Institute ofTechnology. 24I —is glamorous. Neuropsychologists have been fascinated by cortical localization ofthese faculties [4] with the hope that analysis and manipulation of the neocortex would open the way to understanding the mind. Haktead has suggested that the frontal lobes could be called "the organs ofcivilization" [5]. Even the wise founder ofAmerican neuropsychology, Karl Lashley, entitled his first monograph "Brain Mechanisms and Intelligence ." Only in recent years has analysis ofsubcortical structures and simpler elements of behavior become more popular among neuropsychologists . My assumption in arguing for a greater role of the fish as a medium of such research is that more study of simpler elements of behavior common to all vertebrates is necessary in order to complement our hitherto one-sided concentration on complex behavior. There are advantages in the relative simplicity of the fish brain. For example, if we wish to record electrical events in the brain, there are fewer neurons to sample in the fish than in mammalian subjects. Therefore , the extent ofneural interaction will be more restricted in this simpler brain. It does not follow that individual neurons are "simpler" among lower vertebrates. It may be that spinal-cord sensory units within the frog are less specialized than those within the cat [6]. However, such specialization offunction among mammals may only attest to the greater integrative capacities ofcentral mechanisms. It is at this level that the brain ofthe fish inspires less awe than does the cat brain. Another example of"simplicity" in fish is that these creatures may do very well after removal of the major part of the telencephalon [7, 8]. Goldfish solve visual discriminations and maze problems following extirpation ofthis structure as well as do normal subjects. Because mammals are so completely dependent upon the integrity ofvarious telencephalic structures, the study of perception and memory might be effectively pursued in an organism where the forebrain can be largely disregarded. New trends in mammalian research toward specification ofthalamic and midbrain structures subserving learning functions [9] make a comparative neuropsychology appear ever more fruitful. Brain physiology can initially be better correlated with stereotyped components of behavior than with more complex and plastic processes. European ethologists have emphasized the interaction of sensory selectivity and fixed-action patterns in the programming ofanimal behavior [10]. Theyhave also formulated certain relationships among the dominant motives of organisms—including hunger, sex, aggression, and fear (11). 242 DavidJ. Ingle · The Use ofthe Fish in Neuropsychology Perspectives in Biology and Medicine · Winter 196$ The neuropsychologist must understand the morphology and inter-relations ofnatural behavior before he can discover what is modified during the course oflearning. The fish is a good subject with which to explore spontaneous behavior...