Conditional discrimination learning in schizophrenia

76

Abstracts /International Journal of Psychophysiology 25 (I 997) 17-84

Two main parallel systems, magnocellular (Ml and parvocellular (P), originating from different types of retinal ganglion cells, segregate in different portions of the pre-geniculate visual pathways. Their relative contribution to two main cortical streams, dorsal and ventral, is still discussed, but, reasonably, the selective damage to the M or P subcortical system should interfere with specific aspects of cortical processing within one or the other cortical system. We studied the performance of patients affected by compression of the ventral part of the anterior visual pathways and normal controls in two different tasks of apparent motion. The first consisted in detecting small displacements of a low-contrast moving edge (Lee et al., J. Newosci. 13: 1001, 19931, while the second required estimating the visible persistence of moving dots (Hogben and Di Lollo, Percept. & Psycholphys. 38: 450, 1985). In the first task, patients were impaired following parafoveal presentations, particularly in the temporal portion of the visual field, while no group difference was present in the second task. However, in the second task patients showed a reduced suppression of visible persistence at long exposure durations. We hypothesize that these results represent a clear instance of selective impairment of the M system in humans, since A) it is known that, afferents from retinal ganglion cells are segregated by size in the human pre-geniculate visual pathways, with the largest axons in ventral position; these axons presumably belong to the M system; B) patients with a ventral compression behave like P ganglion cells of the macaque monkey, which have previously been shown to exhibit elevated and unmodulated thresholds for apparent motion; and C) patients are less sensitive to the inhibitory signal suppressing visible persistence, that probably comes from the M system. PROBING ATTENTION AND AWARENESS ELECTROMAGNETIC AND FUNCTIONAL ROIMAGING

WITH NEU-

George R. Mangun Department of Psychology, University of California at Davis, Davis, CA 95616, USA Awareness is a dynamic state that depends on both what we elect to pay attention to and what attracts our attention reflexively. When these processes are impaired or dysfunctional - as they are in many neurological and psychiatric diseases - the very thread of consciousness is threatened. Remarkably, our knowledge of how we attend and become aware of selected events and objects in the environment is modest at best. Cognitive theories describe the basic operations of attentional mechanisms in terms of elementary mental operations, but until a detailed neurobiological theory of attention is in our grasp, we will fail in the goal of preventing, diagnosing and treating the disorders of attention that plague humanity. Arriving at such a theory is an immense task, one that is now undertaken with an increasing degree of vigor in humans using modem imaging tools. One of the most exciting

areas of research in this realm is the application of electromagnetic and functional neuroimaging in the study of human attentional mechanisms. These powerful new tools promise to elucidate not only the functional anatomy of the human brain attention system, but also the important temporal orchestration of component processes that is essential for normal brain functioning. In this presentation, I will review our work in combining event-related potentials (ERPs) and positron emission tomography in the study of selective perception and attention in healthy humans.

NEUROMAGNETIC CHARACTERIZATION BRAIN FUNCTIONS

OF HUMAN

Riitta Hari Brain Research Unit, Low Temp. Lab., Helsinki Univ. Technology, 02150 Espoo, Finland Magnetoencephalographic (MEG) signals provide noninvasive and temporally accurate information about the activation of human fissural cortex. Source models and current reconstruction algorithms are used to deduce the underlying current distributions from the measured signal patterns. The present state-of-the-art helmet-shaped devices contain extended sensor arrays so that signals can be picked up rapidly and reliably over the whole scalp. Auditory, somatosensory and visual evoked responses imply activation of several cortical areas, besides the primary projection cortices, during the first 400 ms following the stimulus onset. For example, median nerve stimulation is followed by activation of the contralateral SI cortex, the SII cortices of both hemispheres, the posterior parietal cortex. In addition, the mesial paracentral lobule is activated when the subject pays attention to the stimuli. MEG recordings also imply that the primary somatomotor cortex may be affected bilaterally during unimanual tasks. The cortical rhythms are modified, besides external stimuli, by visual and motor imagery. The different frequency components of the rhythms may have distinct functional roles. For example, the 10 and 20 Hz components of the magnetic mu rhythm, generated in the somatomotor cortex, differ in their timing to stimulation of the peripheral nerves and to voluntary movements. Moreover, the generation site of the 20-Hz rhythm-but not of the lo-Hz rhythm-follows in a somatotopical order the moving body part. Recent studies indicate that the somatomotor rhythms may have a close connection to the rhythmic&y of the moving muscle. CONDITIONAL DISCRIMINATION SCHIZOPHRENIA

LEARNING

IN

K. Dantendorfer*, D. Maierhofer, I. Daum, M. Schugens, P. Anderer, H.V. Semlitsch and H. Katschnig Department of Psychiatry, University of Vienna, Wahringer Giirtel 18-20, A-1090 Vienna, Austria

Abstracts /International Journal of Psychophysiology 25 (1997) 17-84

Recent reports suggest, that memory and learning deficits seem to be more specific to schizophrenia (SZ) than previously accepted. Conditional discrimination learning based on eyelid conditioning has been shown to be selectively sensitive in testing temporal lobe function and has the advantage of making minimal demands on attentional capacities and motivation. In our ongoing study, an eyelid conditional discrimination learning task (Daum et al., Behavioral Neuroscience 1991) is used to examine healthy controls and two groups of SZ patients (DSM-III-R paranoid type SZ with predominant positive symptoms and disorganized type with predominant thought disorders). The occurrence of the first conditioned response (FCR) and response frequency to reinforced (CRR) and unreinforced trials (CRU) are quantified. Two paranoid type SZ patients tested up to now, showed high rates of CRRs as well as CRUs (CRR/CRU; 23%/25% and 29%/21%). On the other hand, the two disorganized type patients showed low rates of CRRs and CRUs (CRR/CRU; 2%/4% and 4%/4%). All four patients had the FCR on unreinforced trials and three of them showed delayed FCRs (trials 9, 14, 171 compared to controls. Our preliminary data suggest, that while paranoid as well as disorganized type schizophrenics show reduced discrimination learning capacity, the two subgroups might be differentiated by conditioned response frequency probably due to differences in temporal lobe functions. Supported by grant no. 5657, Jubililumsfonds der Gsterreichischen Nationalbank. EXPERIENTIAL PHENOMENA ELICITED BY DIRECI ELECTRICAL STIMULATION OF THE BRAIN Eric Halgren* and Patrick Chauvel INSERM, Clinique Neurologique, CHU Pontchaillou, 35033 Rennes, France Brain Research Institute, Neurology W127B, VAMC, West Los Angeles, CA 90073, USA Lacking reasonable alternatives, one may suppose that awareness is embodied in the firing of neurons distributed through wide domains of the association cortex together with related parts of the thalamus and limbic system. The primary exteroceptive cortices provide the classical gateways for information defining this firing-pattern. Other gateways, identified using direct electrical stimulation of the human brain, include the sensory association areas, turning sensation into perception by infusing it with depth, distance, color, etc, the amygdala and other limbic system structures, providing visceral sensations, emotional affects and images to bend the conscious mind toward biological imperatives, the hippocampal formation, retracting the contribution of remembered or imagined events to the contents of awareness; and prefrontal cortex, injecting into awareness thoughts and images, possibly retracing primary memory. These gateways do not have nearly as fixed or topographically precise access to awareness as do the primary exteroceptice cortices. Indeed, the occurrence and content of

77

experiential events after their stimulation is unpredictable, being often more dependent on the subjects’ personality and immediate context that upon the precise topography of stimulation. Considered as a whole, the phenomena evoked by electrical stimulation of the human brain helps to identify and localize the multiple sources of information used by the brain to define mental contents. Supported by ONR, INSERM, NIH and HFSPO PSYCHOPHYSIOLOGY OF THE HUMAN HIPPOCAMPAL FORMATION DURING LEARNING AND MEMORY Eric Halgren* Brain Research Institute, Neurology W127B, VAMC, West Los Angeles, CA 90073, USA INSERM, Clinique Neurologique, CHU Pontchaillou, 35033 Rennes, France Recordings from the human hippocampal formation (HFC) during cognitive tasks (made in the context of evaluation for surgical treatment of medically uncontrolled epilepsy) support the following principles: Hippocampal processing is engaged by a wide variety of cognitive tasks: The HCF generates a large N2/P3b to rare attended stimuli in the visual, auditory and somatosensory modalities. It also generates a large N4/LPC to semantic stimuli such as words and faces, in lexical decision and sentence reading, as well as memory tasks. Thus, the HCF is engaged by stimuli and tasks that have no overt spatial or mnestic aspects. This is consistent with the commonplace observation that experience is continuously encoded into declarative memory, regardless of the explicit task. Metabolic studies clearly underestimate the situations when the HCF is engaged, perhaps because it is engaged in most tasks and thus is eliminated from PET or fMR1 images when two conditions are subtracted. Hippocampal Processing is on-line, interactiL.e and infonnation-specific with the association cotices: The N2/P3b and

N4/LPC are generated in multiple cortical areas simultaneously with the HCF, notably the ventrolateral prefrontal cortex, the cortex of the superior temporal sulcus and cortex in the ventral object-processing stream. HCF neurons fire specifically to particular words or faces in particular context. Thus, the HCF is engaged with various sectors of association cortex from the beginning to the completion of cognitive contextual integration, participating in the creation of neuronal networks specifically encoding cognitive events. Supported by ONR, INSERM, NIF and HFSPO. THE INFLUENCE OF DEXAMETHASONE ON SLOW BRAIN POTENTIALS, HEART-RATE, MOOD AND TASK PERFORMANCE DURING MEMORY TASKS J. Lehmann*, M. Miinstennann, J. Stem, R. Jilrgens, B. Grbzinger and J. Edrich University of Uhn, Dept. of Biomed. Eng. & Div. of Neurophysiol., D 89069 Ulm, Germany