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Neuromagnetic characterization of human brain functions
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 (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