Review| Volume 48, ISSUE 2, P81-98, July 15, 2000

The imbalanced brain: from normal behavior to schizophrenia

  • Stephen Grossberg
    Address reprint requests to Stephen Grossberg, Boston University, Center for Adaptive Systems, 677 Beacon Street, Boston MA 02215
    Department of Cognitive and Neural Systems and Center for Adaptive Systems, Boston University, Boston, Massachusetts, USA
    Search for articles by this author


      An outstanding problem in psychiatry concerns how to link discoveries about the pharmacological, neurophysiological, and neuroanatomical substrates of mental disorders to the abnormal behaviors that they control. A related problem concerns how to understand abnormal behaviors on a continuum with normal behaviors. During the past few decades, neural models have been developed of how normal cognitive and emotional processes learn from the environment, focus attention and act upon motivationally important events, and cope with unexpected events. When arousal or volitional signals in these models are suitably altered, they give rise to symptoms that strikingly resemble negative and positive symptoms of schizophrenia, including flat affect, impoverishment of will, attentional problems, loss of a theory of mind, thought derailment, hallucinations, and delusions. This article models how emotional centers of the brain, such as the amygdala, interact with sensory and prefrontal cortices (notably ventral, or orbital, prefrontal cortex) to generate affective states, attend to motivationally salient sensory events, and elicit motivated behaviors. Closing this feedback loop between cognitive and emotional centers is predicted to generate a cognitive–emotional resonance that can support conscious awareness. When such emotional centers become depressed, negative symptoms of schizophrenia emerge in the model. Such emotional centers are modeled as opponent affective processes, such as fear and relief, whose response amplitude and sensitivity are calibrated by an arousal level and chemical transmitters that slowly inactivate, or habituate, in an activity-dependent way. These opponent processes exhibit an Inverted-U, whereby behavior becomes depressed if the arousal level is chosen too large or too small. The negative symptoms are owing to the way in which the depressed opponent process interacts with other circuits throughout the brain.


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        • Abbott L.F.
        • Varela K.
        • Sen K.
        • Nelson S.B.
        Synaptic depression and cortical gain control.
        Science. 1997; 275: 220-223
        • Aggleton J.P.
        The contribution of the amygdala to normal and abnormal emotional states.
        Trends Neurosci. 1993; 16: 328-333
        • Amaral D.C.
        • Price J.L.
        Amygdalo-cortical projections in the monkey (Macaca fascicularis).
        J Comp Neurol. 1984; 230: 465-496
        • Andreasen N.C.
        Positive and negative symptoms.
        Mod Probl Pharmacopsychiatry. 1990; 24: 1
        • Arndt S.
        • Alliger R.J.
        • Andreasen N.C.
        The distinction of positive and negative symptoms.
        Br J Psychiatry. 1991; 158: 317-322
        • Aston-Jones G.
        • Rajkowski J.
        • Kubiak P.
        • Alexinsky T.
        Locus coeruleous neurons in monkey are selectively activated by attended cues in a vigilance task.
        J Neurosci. 1994; 14: 4467-4480
        • Baddeley A.D.
        Working Memory. Clarendon, Oxford, UK1986
        • Baloch A.
        • Grossberg S.
        • Mingolla E.
        • Nogueira C.A.M.
        Neural model of first-order and second-order motion perception and magnocellular dynamics.
        J Opt Soc Am A. 1999; 16: 953-978
        • Barbas H.
        Anatomic basis of cognitive–emotional interactions in the primate prefrontal cortex.
        Neurosci Biobehav Rev. 1995; 19: 499-510
      1. Bleuler E (1950): Dementia Praecox, or the Group of Schizophrenics [Zinken J, translator]. New York: International Universities Press [original work published 1911].

        • Blumer D.
        • Benson D.F.
        Personality changes with frontal lobe lesions.
        in: Benson D.F. Blumer D. Psychiatric Aspects of Neurological Disease. Grune and Stratton, New York1975: 151-170
        • Bower G.H.
        Mood and memory.
        Am Psychol. 1981; 36: 129-148
        • Bradski G.
        • Carpenter G.A.
        • Grossberg S.
        STORE working memory networks for storage and recall of arbitrary temporal sequences.
        Biol Cybern. 1994; 71: 469-480
        • Braff D.L.
        Attention, habituation, and information processing in psychiatric disorders.
        in: Michael B. Cavenar J.O. Brodie H.K. Psychiatry. Vol 3. Lippincott, Philadelphia1985: 1-12
        • Brown J.L.
        in: Graham C.H. Vision and Visual Perception. Wiley, New York1965: 479-503
        • Buchanan R.W.
        • Strauss M.E.
        • Breier A.
        • Kirkpatrick B.
        • Carpenter W.T.
        Attentional impairments in deficit and nondeficit forms of schizophrenia.
        Am J Psychiatry. 1997; 154: 363-370
        • Bullock D.
        • Cisek P.
        • Grossberg S.
        Cortical networks for control of voluntary arm movements under variable force conditions.
        Cereb Cortex. 1998; 8: 48-62
        • Buonomano D.V.
        • Baxter D.A.
        • Byrne J.H.
        Small networks of empirically derived adaptive elements simulate some higher-order features of classical conditioning.
        Neural Networks. 1990; 3: 507-523
        • Bustillo J.R.
        • Thaker G.
        • Buchanan R.W.
        • Moran M.
        • Kirkpatrick B.
        • Carpenter W.T.
        Visual information-processing impairments in deficit and nondeficit schizophrenia.
        Am J Psychiatry. 1997; 154: 647-654
        • Carlsson A.
        The current status of the dopamine hypothesis of schizophrenia.
        Neuropsychopharmacology. 1988; 1: 179
        • Carpenter G.A.
        • Grossberg S.
        Adaptation and transmitter gating in vertebrate photoreceptors.
        J Theor Neurobiol. 1981; 1: 1-42
        • Carpenter G.A.
        • Grossberg S.
        A neural theory of circadian rhythms.
        Biol Cybern. 1983; 48: 35-59
        • Carpenter G.A.
        • Grossberg S.
        A neural theory of circadian rhythms.
        Am J Physiol. 1984; 247: R1067-R1082
        • Carpenter G.A.
        • Grossberg S.
        A neural theory of circadian rhythms.
        J Theor Biol. 1985; 113: 163-223
        • Carpenter G.A.
        • Grossberg S.
        Integrating symbolic and neural processing in a self-organizing architecture for pattern recognition and prediction.
        in: Honavar V. Uhr L. Artificial Intelligence and Neural Networks Steps Towards Principled Prediction. Academic Press, San Diego1994: 387-421
        • Contreras-Vidal J.L.
        • Grossberg S.
        • Bullock D.
        A neural model of cerebellar learning for arm movement control.
        Learning Memory. 1997; 3: 475-502
        • Cox V.C.
        • Kakolewski J.W.
        • Valenstein E.S.
        Inhibition of eating and drinking following hypothalamic stimulation in the rat.
        J Comp Physiol Psychol. 1969; 68: 530-535
        • Damasio A.R.
        The Feeling of What Happens. Harcourt Brace, New York1999
        • Damasio A.R.
        • Tranel D.
        • Damasio H.
        Somatic markers and the guidance of behavior.
        in: Levin H.S. Eisenberg H.M. Benton A.L. Frontal Lobe Function and Dysfunction. Oxford University Press, Oxford, UK1991: 217-229
        • Davis M.
        The role of the amygdala in emotional learning.
        Int Rev Neurobiol. 1994; 36: 225-265
        • Denny M.R.
        Relaxation theory and experiments.
        in: Brush F.R. Aversive Conditioning and Learning. Academic Press, New York1971: 235-295
        • Desimone R.
        Face-selective cells in the temporal cortex of monkeys.
        J Cogn Neurosci. 1991; 3: 1-8
        • Dews P.B.
        Studies on behavior, IV.
        J Pharmacol Exp Ther. 1958; 122: 137-147
        • Early T.S.
        • Haller J.W.
        • Posner M.I.
        • Raichle M.
        The left striato-pallidal hyperactivity model of schizophrenia.
        in: David A.S. Cutting J.C. The Neuropsychology of Schizophrenia. Erlbaum, Hillsdale, NJ1994: 15-37
        • Estes W.K.
        • Skinner B.F.
        Some quantitative properties of anxiety.
        J Exp Psychol. 1941; 29: 390-400
        • Evarts E.V.
        Motor cortex reflexes associated with learned movement.
        Science. 1973; 179: 501-503
        • Felleman D.J.
        • van Essen C.D.
        Distributed hierarchical processing in the primate cerebral cortex.
        Cereb Cortex. 1991; 1: 1-47
        • Fiala J.C.
        • Grossberg S.
        • Bullock D.
        Metabotropic glutamate receptor activation in cerebellar Purkinje cells as substrate for adaptive timing of classically conditioned eye blink response.
        J Neurosci. 1996; 16: 3760-3774
        • Francis G.
        • Grossberg S.
        Cortical dynamics of boundary segmentation and reset.
        Perception. 1996; 25: 543-567
        • Francis G.
        • Grossberg S.
        Cortical dynamics of form and motion integration.
        Vision Res. 1996; 36: 149-173
        • Francis G.
        • Grossberg S.
        • Mingolla E.
        Cortical dynamics of feature binding and reset.
        Vision Res. 1994; 34: 1089-1104
        • Frith C.D.
        The Cognitive Neuropsychology of Schizophrenia. Erlbaum, Hillsdale, NJ1992
        • Frith C.D.
        Theory of mind in schizophrenia.
        in: David A.S. Cutting J.C. The Neuropsychology of Schizophrenia. Erlbaum, Hillsdale, NJ1994: 147-161
        • Fulton J.F.
        Frontal Lobotomy and Affective Behavior. Norton, New York1950
        • Fuster J.M.
        The Prefrontal Cortex. 2nd ed. Raven, New York1989
        • Gloor P.
        • Olivier A.
        • Quesney L.F.
        • Andermann F.
        • Horowitz S.
        The role of the limbic system in experiential phenomena of temporal lobe epilepsy.
        Ann Neurol. 1982; 12: 129-144
        • Gochin P.M.
        • Miller E.K.
        • Gross C.G.
        • Gerstein G.L.
        Functional interactions among neurons in inferior temporal cortex of the awake macaque.
        Exp Brain Res. 1991; 84: 505-516
        • Grace A.A.
        Phasic versus tonic dopamine release and the modulation of dopamine system responsivity.
        Neuroscience. 1991; 41: 1-24
        • Grossberg S.
        Some physiological and biochemical consequences of psychological postulates.
        Proc Natl Acad Sci U S A. 1968; 60: 758-765
        • Grossberg S.
        On the production and release of chemical transmitters and related topics in cellular control.
        J Theor Biol. 1969; 22: 325-364
        • Grossberg S.
        On the dynamics of operant conditioning.
        J Theor Biol. 1971; 33: 225-255
        • Grossberg S.
        A neural theory of punishment and avoidance, I.
        Math Biosci. 1972; 15: 39-67
        • Grossberg S.
        A neural theory of punishment and avoidance, II.
        Math Biosci. 1972; 15: 253-285
        • Grossberg S.
        Contour enhancement, short term memory, and constancies in reverberating neural networks.
        Stud Appl Math. 1973; 52: 217-257
        • Grossberg S.
        A neural model of attention, reinforcement, and discrimination learning.
        Int Rev Neurobiol. 1975; 18: 263-327
        • Grossberg S.
        Behavioral contrast in short term memory.
        J Math Psychol. 1978; 3: 199-219
        • Grossberg S.
        A theory of human memory.
        in: Rosen R. Snell F. Progress in Theoretical Biology. Academic Press, New York1978: 233-374
        • Grossberg S.
        How does a brain build a cognitive code?.
        Psychol Rev. 1980; 1: 1-51
        • Grossberg S.
        Associative and competitive principles of learning and development.
        in: Amari S.I. Arbib M. Competition and Cooperation in Neural Networks. Springer-Verlag, New York1982: 295-341
        • Grossberg S.
        Processing of expected and unexpected events during conditioning and attention.
        Psychol Rev. 1982; 89: 529-572
        • Grossberg S.
        Some normal and abnormal behavioral syndromes due to transmitter gating of opponent processes.
        Biol Psychiatry. 1984; 19: 1075-1118
        • Grossberg S.
        Some psychophysiological and pharmacological correlates of a developmental, cognitive, and motivational theory.
        in: Karrer R. Cohen J. Tueting P. Brain and Information Event Related Potentials. New York Academy of Sciences, New York1984: 58-142
        • Grossberg S.
        The Adaptive Brain. Vol I. Elsevier/North-Holland, Amsterdam1987
        • Grossberg S.
        Cortical dynamics of three-dimensional form, color, and brightness perception, II.
        Perception Psychophys. 1987; 41: 117-158
        • Grossberg S.
        The link between brain learning, attention, and consciousness.
        Conscious Cogn. 1999; 8: 1-44
      2. Grossberg S (in press): How hallucinations may arise from brain mechanisms of learning, attention, and volition. J Int Neuropsychol Soc.

        • Grossberg S.
        • Gutowski S.
        Neural dynamics of decision making under risk.
        Psychol Rev. 1987; 94: 300-318
        • Grossberg S.
        • Levine D.S.
        Neural dynamics of attentionally modulated Pavlovian conditioning.
        Appl Opt. 1987; 26: 5015-5030
        • Grossberg S.
        • Merrill J.W.L.
        A neural network model of adaptively timed reinforcement learning and hippocampal dynamics.
        Cogn Brain Res. 1992; 1: 3-38
        • Grossberg S.
        • Merrill J.W.L.
        The hippocampus and cerebellum in adaptively timed learning, recognition, and movement.
        J Cogn Neurosci. 1996; 8: 257-277
        • Grossberg S.
        • Schmajuk N.A.
        Neural dynamics of attentionally-modulated Pavlovian conditioning.
        Psychobiology. 1987; 15: 195-240
        • Grossberg S.
        • Stone G.
        Neural dynamics of attention switching and temporal order information in short term memory.
        Memory Cogn. 1986; 14: 451-468
        • Halgren E.
        • Walter R.D.
        • Cherlow D.G.
        • Crandall P.H.
        Mental phenomena evoked by electrical stimulations of the human hippocampal formation and amygdala.
        Brain. 1978; 101: 83-117
        • Harries M.H.
        • Perrett D.I.
        Visual processing of faces in temporal cortex.
        J Cogn Neurosci. 1991; 3: 9-24
        • Heinrichs R.W.
        Schizophrenia and the brain.
        Am Psychol. 1993; 48: 221-233
        • Horak R.B.
        • Anderson M.E.
        Influence of globus pallidus on arm movements in monkeys, I.
        J Neurophysiol. 1984; 52: 290-304
        • Horak R.B.
        • Anderson M.E.
        Influence of globus pallidus on arm movements in monkeys, II.
        J Neurophysiol. 1984; 52: 305-322
        • Hornykiewicz O.
        Parkinsonism induced by dopaminergic antagonists.
        in: Calne D.B. Barbeau A. Advances in Neurology. Vol 9. Raven, New York1975
        • Ito M.
        The Cerebellum and Neural Control. Raven, New York1984
        • Kalaska J.F.
        • Cohen D.A.D.
        • Hyde M.L.
        • Prud’homme M.J.
        A comparison of movement direction-related versus load direction-related activity in primate motor cortex using a two-dimensional reaching task.
        J Neurosci. 1989; 9: 2080-2102
        • Kamin L.J.
        “Attention-like” processes in classical conditioning.
        in: Jones M.R. Miami Symposium on the Prediction of Behavior Aversive Stimulation. University of Miami Press, Miami1968: 9-31
        • Kamin L.J.
        Predictability, surprise, attention and conditioning.
        in: Campbell B.A. Church R.M. Punishment and Aversive Behavior. Appleton-Century-Crofts, New York1969: 279-298
      3. Kraepelin E (1919): Dementia Praecox and Paraphrenia [Barclay RM, translator]. Edinburgh: ES Livingston [original work published 1913].

        • Kuhar M.J.
        • Atweh S.F.
        • Bird S.J.
        Studies of cholinergic-monoaminergic interactions in rat brain.
        in: Butcher L.L. Cholinergic-Monoaminergic Interactions in the Brain. Academic Press, New York1978
        • LeDoux J.E.
        Emotional memory systems in the brain.
        Behav Brain Res. 1993; 58: 69-79
        • Leibowitz S.F.
        Adrenergic receptor mechanisms in eating and drinking.
        in: Schmitt F.O. Worden F.G. The Neurosciences Third Study Program. MIT Press, Cambridge, MA1974
        • Liddle P.F.
        Volition and schizophrenia.
        in: David A.S. Cutting J.C. The Neuropsychology of Scizophrenia. Erlbaum, Hillsdale, NJ1994: 39-49
        • Lloyd K.G.
        Observations concerning neurotransmitter interaction in schizophrenia.
        in: Butcher L.L. Cholinergic–Monoaminergic Interactions in the Brain. Academic Press, New York1978
        • Lynch M.E.
        Schizophrenia and the D1 receptor.
        Progr Neuropsychopharmacol Biol Psychiatry. 1992; 16: 797
      4. Macchi G, Rinvik E (1976): Thalamo-telencephalic circuits: A neuroanatomical survey. In: Rémond A, editor. Handbook of Electroencephalography and Clinical Neurophysiology, Vol 2, Part A. Amsterdam: Elsevier.

        • Markram H.
        • Lübke J.
        • Frotscher M.
        • Sakmann B.
        Regulation of synaptic efficacy by coincidence of postsynaptic APs and EPSPs.
        Science. 1997; 275: 213-215
        • Markram H.
        • Tsodyks M.
        Redistribution of synaptic efficacy between neocortical pyramidal neurons.
        Nature. 1996; 382: 807-810
        • Marrocco R.T.
        • Witte E.A.
        • Davidson M.C.
        Arousal systems.
        Curr Opin Neurobiol. 1994; 4: 166-170
        • Masterson F.A.
        Is termination of a warning signal an effective reward for the rat?.
        J Comp Physiol Psychol. 1970; 72: 471-475
        • McAllister W.R.
        • McAllister D.E.
        Behavioral measurement of conditioned fear.
        in: Brush F.R. Aversive Conditioning and Learning. Academic Press, New York1971: 105-179
        • McAllister W.R.
        • McAllister D.E.
        The inverse relationship between shock intensity and shuttlebox avoidance learning in rats.
        J Comp Physiol Psychol. 1971; 74: 426-433
        • Mirsky A.F.
        Neuropsychological bases of schizophrenia.
        Annu Rev Psychol. 1969; 20: 321-348
        • Mishkin M.
        • Aggleton J.
        Multiple functional contributions of the amygdala in the monkey.
        in: Ben-Ari Y. The Amygdaloid Complex. Elsevier, Amsterdam1981: 409-420
        • Netter P.
        • Rammsayer T.
        Reactivity to dopaminergic drugs and aggression related personality traits.
        Pers Individual Differ. 1991; 12: 1009-1017
        • Ögmen H.
        A neural theory of retino-cortical dynamics.
        Neural Networks. 1993; 6: 245-273
        • Ögmen H.
        • Gagné S.
        Neural network architectures for motion perception and elementary motion detection in the fly visual system.
        Neural Networks. 1990; 3: 487-505
        • Pantelis C.
        • Harvey C.
        • Taylor J.
        • Campbell P.G.
        The anterior cingulate mediates processing selection in the Stroop attentional conflict paradigm.
        Proc Natl Acad Sci U S A. 1991; 87: 256-259
        • Passingham R.E.
        The Frontal Lobes and Voluntary Action. Oxford University Press, Oxford, UK1997
        • Pavlov I.P.
        Conditioned Reflexes. Oxford University Press, London1927
        • Pilowsky I.
        • Bassett D.
        Schizophrenia and the response to facial emotions.
        Compr Psychiatry. 1980; 21: 515-526
        • Rammsayer T.
        • Netter P.
        • Vogel W.
        A neurochemical model underlying differences in reaction times between introverts and extraverts.
        Pers Individual Differ. 1993; 14: 701-712
        • Reynierse J.H.
        • Rizley R.C.
        Relaxation and fear as determinants of maintained avoidance in rats.
        J Comp Physiol Psychol. 1970; 72: 223-232
        • Reynolds G.P.
        Increased concentrations and lateral asymmetry of amygdala dopamine in schizophrenia.
        Nature. 1983; 305: 527-529
        • Reynolds G.P.
        Post-mortem neurochemical studies in human postmortem brain tissue.
        in: Hafner H. Gattaz W.F. Janzarik W. Search for the Causes of Schizophrenia. Springer, Heidelberg, Germany1987: 236-240
        • Reynolds G.S.
        A Primer of Operant Conditioning. Scott, Foresman, Glenview, IL1968
        • Riklan M.
        L-dopa and Parkinsonism. C.C. Thomas, Springfield, IL1973
        • Robbins T.W.
        • Everitt B.J.
        Arousal systems and attention.
        in: Gazzaniga M.S. Handbook of Cognitive Neuroscience. MIT Press, Cambridge, MA1995
        • Rolls E.T.
        The orbitofrontal cortex.
        in: Roberts A.C. Robbins T.W. Weiskrantz L. The Prefrontal Cortex Executive and Cognitive Functions. Oxford University Press, Oxford, UK1998: 67-86
        • Sauer H.
        • Geider F.J.
        • Binkert M.
        • Reitz C.
        • Schroder J.
        Is chronic schizophrenia heterogeneous?.
        Biol Psychiatry. 1991; 29: 661S
        • Sekuler R.
        Visual motion perception.
        in: Carterette E.D. Friedman M.P. Handbook of Perception. Vol V. Academic Press, San Diego1975: 387-433
        • Sillito A.M.
        • Jones H.E.
        • Gerstein G.L.
        • West D.C.
        Feature-linked synchronization of the thalamic relay cell firing induced by feedback from the visual cortex.
        Nature. 1994; 369: 479-482
        • Staddon J.E.R.
        Adaptive Behavior and Learning. Cambridge University Press, New York1983
        • Stevens J.
        An anatomy of schizophrenia?.
        Arch Gen Psychiatry. 1993; 29: 177-189
        • Swanson J.M.
        • Kinsbourne M.
        Stimulant-related state-dependent learning in hyperactive children.
        Science. 1976; 192: 1354-1356
        • Tecce J.J.
        • Cole J.O.
        Amphetamine effects in man.
        Science. 1974; 185: 451-453
        • Thompson R.F.
        The neural basis of basic associative learning of discrete behavioral responses.
        Trends Neurosci. 1988; 11: 152-155
        • Torrey E.
        • Peterson M.
        Schizophrenia and the limbic system.
        Lancet. 1974; II: 942-946
      5. Tsodyks M, Pawelzik K, Markram H (in press): Neural networks with dynamic synapses. Neural Comput.

        • Tsumoto T.
        • Creutzfeldt O.D.
        • Legéndy C.F.
        Functional organization of the corticofugal system from visual cortex to lateral geniculate nucleus in the cat.
        Exp Brain Res. 1978; 32: 345-364
        • Turner B.H.
        • Mishkin M.
        • Knapp M.
        Organization of the amygdalopetal projections from modality-specific cortical association areas in the monkey.
        J Comp Neurol. 1980; 191: 515-643
        • Ungerleider L.G.
        • Mishkin M.
        Two cortical visual systems.
        in: Ingle D.L. Goodale M.A. Mansfield R.J.W. Analysis of Visual Behavior. MIT Press, Cambridge, MA1982: 549-586
        • Valenstein E.S.
        • Cox V.C.
        • Kakolewski J.W.
        The hypothalamus and motivated behavior.
        in: Tapp J.T. Reinforcement and Behavior. Academic Press, New York1969: 242-285
        • von Helmholtz H.
        Handbuch der Physiologischen Optik. Voss, Hamburg1866
      6. von Helmholtz H (1962): Physiological Optics, Vol 2 [Southall JP, translator]. New York: Dover.

        • Wallach M.B.
        Drug-induced stereotyped behavior.
        in: Usdin E. Neurophyshopharmacology of Monoamines and their Regulatory Enzymes. Raven, New York1974
        • Weinberger D.F.
        Schizophrenia and the frontal lobe.
        Trends Neurosci. 1988; 11: 367-370
        • Weiss G.
        • Hechtman L.
        The hyperactive child syndrome.
        Science. 1979; 205: 1348-1354
        • Wilson F.A.W.
        • Scalaidhe O.
        • Goldman-Rakic P.S.
        Dissociation of object and spatial processing domains in primate prefrontal cortex.
        Science. 1993; 260: 1955-1958
        • Wolgin D.L.
        • Cytawa J.
        • Teitelbaum P.
        The role of activation in the regulation of food intake.
        in: Novin D. Wyrwicka W. Bray G. Hunger Basic Mechanisms and Clinical Implications. Raven, New York1976
        • Zuckerman M.
        Sensation seeking.
        Behav Brain Sci. 1984; 7: 413-471