From effects to systems in neuropsychology
DOI:10.1093/acprof:oso/9780199228768.003.0022
Abstract and Keywords
This chapter looks at changes and developments in the study of effects in neuropsychology. It highlights the shift in the study of effects from focusing on specific brain parts to the whole nervous system. This shift was influenced by the increase interest in activity in and across several loci spurred by the development of brain imaging methodology and the results of original study of effects themselves which stimulated analysis in terms of systems.
Tracing changes is a complex matter—analysis of behavioural change is difficult enough, let alone conceptual change. Neuropsychology today is in many ways strikingly different from when I entered the field, but in other ways (at least for the visual system) many of the issues are not all that different from the days of William James or David Ferrier or Luigi Luciani or Hermann Munk. My entrée into neuropsychology was in some ways an accident. I started my undergraduate studies at Swarthmore College as a Physics major, but was drafted into the army in my third year, in 1944. When I returned from overseas service, and bolstered by the ‘GI Bill’ (which covered tuition and other fees of veterans), I thought a broader education would be welcome and actually possible. Swarthmore at the time had a very strong and interesting psychology department—Wolfgang Köhler, Solomon Asch, David Krech, Hans Wallach, among others—and I had a roommate, Mike, who was a son of Max Wertheimer and whose sister, Lise, was also a student there. I became a family friend of both of them. And so, after some dithering, I started afresh and decided to read Psychology, but, given the history of the war and other horrors, such as the Holocaust and the widespread racial prejudice, I thought Social Psychology would be the most useful and challenging. For graduate work (after a gratuitous MSc stint at Oxford) I took the tough road for my PhD to the Department of Experimental Psychology at Harvard, because I wanted to get a solid base in experimental method before going to the socially complex domain.
The career accident occurred when I was suddenly invited to teach a course in physiological psychology at Tufts University. Their lecturer had become ill and they appealed to the Harvard Department for an instant replacement for a course already in progress. As I had taken that course at Harvard, they recommended me. I managed to stay ahead of the class by a page or two of Morgan's textbook, but became deeply engrossed in the subject and never looked back. My PhD with Karl Pribram and collaborations with him and colleagues, (p.278) especially Mort Mishkin, more or less sealed the matter. My translation to the UK came when, out of the blue, a post-doctoral fellowship was awarded me by the US National Academy—I had not applied for it, and had not even known of its existence. I choose to go to Oxford for a year to learn about silver staining, a difficult but important method then in neuronal tracing, with Paul Glees in the Oxford Physiology Department. From there, various unanticipated invitations and appointments arose.
My PhD thesis was typical of what neuropsychologists (except that then we were called physiological psychologists) would do at that time. It was the study of an effect. In my case it was the effect of a lesion of the amygdala in the monkey and, a bit later, the effects of occipital, inferotemporal, and frontal lesions, in both monkeys and people. Effects were surprising and eventful stuff back then. Karl Lashley was the dominant figure in the field, and his theories of mass action and equipotentiality were much to the fore. He allowed some specialization in the brain for sensory-receiving and motor areas, but the rest was a non-specialized conglomerate in which the size of the lesion was all that mattered. As it happens, I attended his graduate seminar courses at Harvard, and it was hard not to be overwhelmed by his incredible erudition and charisma—was there nothing he did not know!—and not to be floored by the sheer mass of his weekly reading assignments. This lanky, ectomophic figure clearly did not like his trips to the North from Orange Park in Florida; he appeared in the department in Memorial Hall buried in a heavy fur-lined coat, emitting dark and persistently clinging smoke from an obscure brand of Turkish cigarette. It is a bit ironic that the evidence from the Pribram Lab, perhaps more than any other, first put the nail in his theoretical coffin—ironic because Pribram was an admirer and had been influenced deeply by Lashley. Pribram had been practising as a clinical neurosurgeon and recounted his surprise to learn that Lashley was still alive, and so went to Orange Park to work with him. Lashley had tried to localize the memory trace, but had failed, and suggested memory was subserved by the mass of cortical tissue that was not specialized for sensory or motor function. But it was discovered by Pribram and Mishkin, amongst other things, that lesions of the inferotemporal cortex in the monkey would interfere specifically with visual learning and memory, and with nothing else, and that parietal lesions would similarly effect tactile tasks. I happened to be in the lab when Lashley visited it and was told about the inferotemporal lesion evidence, which he suggested—a bit weakly—might just be a diminution of visual attention. Lashley was a great man; he was wrong about some important theoretical issues, but he was gloriously wrong in the sense that he was one of the first to tell us how and what to find out, and he was an unforgettable teacher.
(p.279) Later, from several labs, the evidence for specific lesion effects mounted—it emerged that hippocampal lesions would have a devastating effect on what later became called episodic memory, and that frontal lobe lesions would interfere with short-term memory, or what later became called working memory, basal ganglion lesions on motor skills, etc. ‘Raw’ effects were turning up both in the animal work and in the human clinic. Indeed, in the clinic the effects were used as diagnostic tools—for example, visual prototype deficits point to parietal lobe lesions, memory problems to medial temporal lobe lesions, and so forth. This was before the days of good CT scanning or ERP recordings and long before the days of MRI, and the neuropsychological evidence was clinically valuable. But no line of historical demarcation can be absolute. Even in those early days of‘effect studies’ there was talk of the ‘Papez Circuit’ for the control of emotion.
Given the robustness of the evidence for specific lesion effects, questions of interpretation and inferences came to the fore. It was widely agreed that the function being interfered with by a lesion was not simply its complementary. As Richard Gregory pointed out forcefully, a transistor that made a radio squeak when removed was not simply inhibiting a squeak function. On the other hand, when double dissociation was obtained (if task A but not task B was affected by lesion I, and task B but not task A was affected by lesion II) reasonable grounds were available for an inference of the two underlying systems being independent. Closer argument led to the conclusion that double dissociation of lesion effects was a necessary but not a sufficient basis for inferences of independence.
But the study of effects became even more interesting when they turned out to be incomplete. For example, it emerged that patients with devastating memory deficits, associated with hippocampal damage or the severe alcoholic toxic effects in Korsakoff's disease, could actually show good storage and retention of material when tested with priming or other methods, although they insisted that they could not remember anything about the material (or the investigator, for that matter). From this came the birth of implicit memory. Lesions of the occipital lobe in the monkey turned out to be less devastating than was thought possible given the apparent blindness that ensued, and in human patients the residual visual function and capability became known as blindsight. Similar phenomena were turning up across the whole spectrum of neuropsychological effects: aphasic patients could show both semantic and syntactic processing, neglect patients could respond to events in their left fields, prosopagnosic patients could show autonomic effects to familiar faces, and so forth (Weiskrantz, 1997). In all cases, the residual function occurred without the awareness by the patients (Weiskrantz, 1991), who hence (p.280) became candidates for the study of neural bases of conscious awareness. Of course, as with all counterintuitive phenomena, a host of counter-suggestions were advanced, for example that the ‘implicit’ or ‘unconscious’ phenomena were merely weaker versions of the explicit or conscious, qualitatively unchanged. Or that subjects' criteria, in signal detection terms, had become more conservative or, in the case of blindsight, that the cortical lesions in the clinical cases were patchy and incompletely, or that there was stray light sneaking into the intact visual field from the hemi-anopically blind one. After much work, the implicit phenomena remain intact. Meanwhile, the study of similar effects in animals has opened up, with evidence, for example, of blindsight in monkeys and also in the construction of tasks that reflect an explicit memory system.
Effects are still being pursued, for instance in the use of transcranial magnetic stimulation (TMS) to attempt to simulate the effects of cortical damage but in a reversible manner (anticipated many years earlier by demonstrations that pulsed electrical stimulation of the frontal cortex could reliably and reveribly simulate the effects of lesions on delayed response tasks (Weiskrantz et al., 1960)), and anodal changes in resting cortical potential could reversibly simulate the effect of visual cortical lesions (Ward and Weiskrantz, 1969), and, of course, in the domain of psychopharmacology where treatments with transmitters are used to counter known effects of specific brain damage, as in Parkinson's disease. But the ‘raw’ spectrum of effects of early neuropsychology is now more or less complete, at least for the cerebral cortex, and treatment effects such as TMS are now cast in a specific search for an answer to specific experimental questions, such as whether stimulating a particular region before or after stimulation of another region can throw light on a processing sequence. There remains, of course, a whole host of effects to be pursued for subcortical loci that are opening up with the study of deep brain stimulation in the treatment of clinical conditions, the pathology of which is rooted in deeper structures. (William James had speculated whether the consciousness of the ‘lower optical centres’ could mix with that which accompanies cortical activity—perhaps we may be able to make a start on that question.) But today the major focus has turned to the study of systems.
There are many reasons for the shift. Firstly, the brain imaging methodology more or less imposes an interest in activity in and across several loci. Secondly, the results of original study of effects themselves stimulate analysis in terms of systems. For example, blindsight evidence highlights the importance of parallel visual pathways for visual processing, especially the midbrain extra-striate pathways. Similarly, effects of occipital damage yielded a strong interest in an early version of ‘two visual systems’. The effects of parietal versus temporal lobe damage, together with the study of agnosia, led to the contrast between the dorsal versus ventral visual systems. Multiple memory systems have (p.281) emerged from the study of dissociable memory deficits, raising questions, for example, of whether there is a frontal system that is important for working memory, the hippocampus and adjoining structures for explicit memory. Thirdly, the cognitive horizons themselves have expanded, and box-and-arrow conceptual diagrams in information-processing terms coincided with the onset of the study of lesion effects. The evidence from neuropsychological cases could directly affect the validity of such diagrams; for example, it could not be that short-term memory flowed into long-term memory in a serial fashion, because they could be doubly dissociated neuropsychologically.
I would have been bold, when I started my career more than 50 years ago, to admit to an interest in the neurology of conscious awareness. Indeed, when during my MSc stint as a graduate student in Oxford, Oliver Zangwill submitted a paper for me to the Quarterly Journal of Experimental Psychology (in my name—perhaps he was the bold one, not I) reporting surprising visual aftereffects of fixation of ‘imaginary’ visual stimuli, the Journal's editor called me aside a few weeks later and reported that, as Zangwill liked the paper, he would of course accept it, but somewhat archly recommended that I should think carefully about my future career. (I asked him to publish and he did, in 1950.) Not only the study of implicit processing in neuropsychology, but also the interests of philosophers, physicists, neurologists, cognitive psychologists, and others in a possible scientific basis for consciousness, have made an active entrée into the domain of systems analysis and discussion. The effect of graduation from effects to systems is exciting because completely new frontiers and methods are emerging, ever in flux. The challenges are much greater than the reporting of effects, as great as these were, because we now have an infinite number of degrees of freedom, and we are still not at the stage of theorizing such that imaging results can be crucial for disconfirmation. But the empirical advances have been stimulating; it has become possible, for example, in blind-sight cases to conduct fMRI measurements of the brain structures that are active when the subjects are visually aware; these can be contrasted directly, and with performance matched, with those that are active when they report no awareness (Sahraie et al. 1997). Knowledge of the structures that are implicated for explicit versus implicit domains, combined with increasing knowledge of the anatomical network within which they are enmeshed, holds promise for advancing both the neural and the theoretical basis of classical issues that once were thought to be intractable to scientific enquiry.
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