Roslyn Holly Fitch (1996) Reconciling the Optimal Brain With Variability. Psycoloquy: 7(03) Optimal Cognition (2)

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PSYCOLOQUY (ISSN 1055-0143) is sponsored by the American Psychological Association (APA).
Psycoloquy 7(03): Reconciling the Optimal Brain With Variability

Commentary on Worden on Optimal-Cognition

Roslyn Holly Fitch
Center for Molecular and Behavioral Neuroscience
Rutgers University
197 University Ave.
Newark, NJ 07102


The concept of an optimal brain which underlies an optimal cognitive strategy for a given species in a given situation is apparently at odds with the enormous within-species variation in cortical organization and cognitive function, and specifically with replicable group differences in brain organization and/or cognitive performance. One such example concerns sex differences in neural lateralization and spatial navigation strategy; differences which cannot be reconciled with the notion of an optimal evolutionary path. Moreover, on a more general level the term "optimal" seems impossible to define with respect to human cognitive behavior, since a specific outcome can rarely be defined as the "ideal" one.


Bayes, conditioning, evolution, foraging, navigation, neural nets, optimality, representation, situated action.
1. Worden (1996) presents evidence for the intriguing argument that an optimal cognitive strategy can be delineated for any given species (presumably including humans) in any given situation. He also presents evidence for the existence of an optimal brain which serves as a biological substrate for the optimal strategy employed. Worden suggests that, unlike computational approaches which tend to be solution-driven, his model proceeds from the point of biological requirement and works backwards to describe processes which may underlie evolution of this optimal brain. In accounting for existing biological data, however, there remains a rather unsettling point which he has not addressed: group differences in neural organization and cognitive strategy within a species, such as those which occur as a function of sex. I will address two specific examples of consistent and replicable sex differences in brain organization and cognitive strategy, and ask how these differences can be fit within the constructs of Worden's model.

2. The first entails sex differences in patterns of cortical lateralization. Evidence showing that male brains are more lateralized than female brains has accumulated at both the structural (Kulynych et al., 1994) and functional (Kimura & Harshman, 1984; McGlone, 1980; Shaywitz et al., 1995; Wood et al., 1991) level in humans, and even in non-human species (Diamond et al., 1981; Fitch et al., 1993; Stewart & Kolb, 1988). Nevertheless, we have no clue regarding the evolutionary basis for this difference. Some have argued that one pattern of organization must represent a "more-evolved" pattern (e.g., one pattern must be superior). The specific assertion that more-lateralized represents more-evolved is grounded in comparative neurophysiology which demonstrates increasing cerebral laterality as one moves up the species ladder. Yet neuropathological evidence suggests that women are at a considerable advantage in cognitive recovery following unilateral damage (McGlone, 1980), a principle which may apply on a larger scale since female newborns also show better cognitive recovery from cortical damage than males (Raz et al., 1995). Thus evolutionary advantage for one pattern of cortical organization within one gender is not particularly clear. Another hypothesis suggests that a given pattern of lateralization may confer advantage in some situations and not others. For example, reference has been made to both the slight female advantage in verbal fluency and the consistent male advantage for spatial tasks like mental rotation, with the implication that bilateral representation is advantageous to verbal tasks and disadvantageous to spatial ones (see Halpern, 1990, for discussion). I appeal to Worden to explain how these complex differences can be reconciled with the notion of an optimal human brain.

3. Secondly, evidence shows that the two sexes can use significantly different cognitive strategies on the same task. Worden presents a somewhat simplified view of the requirements inherent to a spatial navigation task. But a careful series of studies with male and female rats showed that the sexes (within this species) use significantly different strategies to solve a maze problem (see Williams & Meck, 1991). Specifically, female rats apparently rely on both geometric and landmark cues, while males rely almost exclusively on geometric cues. The male pattern appears to confer advantage during initial learning, since males learn the maze faster and with fewer errors. But when the spatial cues within the maze are altered, females performance is, overall, significantly better. The interpretation is that females take longer to learn the maze because they are assimilating more information, which later facilitates performance in the advent of change. Again, I leave it to Worden to explain how these differences can be reconciled with a his model for a single optimal cognitive strategy for a given task, within a species.

4. Such findings may never be shown to reflect evolutionary advantage for one sex or another, but rather, may reflect the general notion that evolution favors variability within a population. The assertion that variability is desirable for a population -- of which the individual is part -- is largely at odds with Worden's hypothesis that evolution should lead to an optimal brain for any species.

5. Finally, I believe that the argument for an "optimal brain," though appealing in some respects for its simplicity, can lead to nothing but trouble when applied to the enormous complexity inherent in "real world brains." Indeed the issue of defining "optimal" has plagued cognitive neuroscience over the past decade, since the measurement and analysis of intelligence (the pinnacle of human cognition) is confounded by subjectivity in definition, measurement, and interpretation. Moreover, the application of the logical constraint that "best" must constitute the action which underlies the ideal outcome is sullied with subjectivity when the "ideal outcome" must be defined. Very few applications of human cognitive behavior produce clear-cut outcomes like "hungry," "satisfied," or "dead" (Worden, 1996). In sum, the word "optimal" implies a value judgment which is acceptable in mathematical modeling, but a conundrum in the real world.


Diamond, M.C., Dowling, G.A., & Johnson, R.E. (1981). Morphological cerebral cortical asymmetry in male and female rats. Experimental Neurology, 71, 261-268.

Fitch, R.H., Brown, C., O'Connor, K. & Tallal, P. (1993). Functional lateralization for auditory temporal processing in male and female rats. Behavioral Neuroscience, 107, 844-850.

Halpern, D.F. (1990). Sex Differences in Cognitive Abilities. Lawrence Erlbaum Associates, London.

Kimura, D. & Harshman, R. (1984). Sex differences in brain organization for verbal and non-verbal functions. In G.J. DeVries et al. (Eds.), Progress in Brain Research, vol. 61. Elsevier Science Publishers, Amsterdam.

Kulynych, J.J., Vladar, K., Jones, D.W., & Weinberger, D.R. (1994). Gender differences in the normal lateralization of the supratemporal cortex: MRI surface-rendering morphometry of Heschl's gyrus and the planum temporal. Cerebral Cortex, 4, 107-118.

McGlone, J. (1980). Sex differences in human brain asymmetry: a critical review. The Behavioral and Brain Sciences, 3, 215-263.

Raz, S., Lauterbach, M.D., Hopkins, T.L., Glogowski, B.K., Porter, C.L., Riggs, W.W. & Sander, C.G. (1995) A female advantage in recovery from early cerebral insult. Developmental Psychology, 31, 958-966.

Shaywitz, B.A., Shaywitz, S.E., Pugh, K.R., Constable, R.T., Skudlarski, P., Fulbright, R.K., Bronen, R.A., Fletcher, J.M., Shankwelier, D.P., Katz, L., & Gore, J.C. (1995) Sex differences in the functional organization of the brain for language. Nature, 373, 607-609.

Stewart, J. & Kolb, B. (1988). Asymmetry in the cerebral cortex of the rat: an analysis of the effects of neonatal gonadectomy on cortical thickness in three strains of rats. Behavioral Neurology and Biology, 49, 344-360.

Williams, C.L., and Meck, W.H. (1991). The organizational effects of gonadal hormones on sexually dimorphic spatial ability. Psychoneuroendocrinolgy, 16, 155-176.

Wood, F.B., Flowers, D.L. & Naylor, C.E. (1991). Cerebral laterality in functional neuroimaging. In F.L. Kitterle (Ed.), Cerebral Laterality: Theory and Research, (pp. 103-116). Lawrence Erlbaum Associates, Hillsdale, New Jersey.

Worden, R.P. (1996). An optimal yardstick for cognition. PSYCOLOQUY 7(1) optimal-cognition.1.worden.

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