31 Neuroelectric signals of working memory predict IQ test scores

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the age ranges as well as scalp. The theoretical implications and clinical utility of these tindings will be discussed.

30 RELATIONSHIP BETWEEN EEG DELTA RESPONSE AND P300 ANALYSED IN SINGLE TRIAL EVENT-RELATED POTENTIALS (ERPS) M. Schiirmarrm(‘), C. Basar-Eroglu(‘~2), V. Kolev(‘,3), E. Basar(tv4) “)Institute of Physiology, Medical University Liibeck, Germany; ‘Z’Institute of Psychology and Cognition Research, Bremen, Germany; ‘3’Bulgarian Academy of Sciences, Sofia, Bulgaria; “‘TUBITAK Brain Dynamics Research Center, Ankara, Turkey According to previous publications, ERPs consist of superimposed alpha, delta, theta and gamma (around 40 Hz) responses [Basar 19801. Such event-related EEG oscillations have been suggested to be “active agents for signal transmission” [Mountcastle 19921. In order to analyse the psychophysiological role of event-related delta oscillations, we studied visual P300 responses. Voluntary healthy subjects underwynt visual evoked potential (VEP) measurements with reversal of a 50’ checkerboard pattern. In a second experiment, two stimuli were applied in pseudorandom order: NON-TARGET (75% occurrence) was checkerboard reversal. Subjects were instructed to pay attention to TARGET (25%) stimuli, i.e. checkerboard reversal with horizontal and vertical displacement by 25’. The data obtained were subjected to ERP frequency analysis, in particular to digital filtering with filter limits chosen adequately according to maxima in the amplitude frequency characteristics [Basar 19801. Filtered averaged ERPs (delta, 0.5-3.5 Hz) showed a prominent positive deflection in TARGET responses at approximately 400 ms. Amplitude differences (VEP vs. TARGET) were significant for delta (p < 0.05, MANOVA) but not for alpha (8-15 Hz) responses. Thus, the delta response is clearly more task-dependent than the alpha response. Filtered single-trial ERPs (0.5-3.5 Hz) were markedly similar to the wide-band filtered curves in the range of 400 ms. Furthermore, we identified subgroups of single-trial ERPs by using the enhancement factor EHF F R/(const* rms) where R is the maximal amplitude of the filtered single-trial ERP and rms is the root mean square value of the filtered prestimulus EEG [Basar 19801. This served two purposes: 1. Identification of single trials with distinct P300 responses: EHF values (filter limits: 0.5-3.5 Hz) were computed for every single trial. The unfiltered average of the subset of “high” EHF trials (above median EHF) showed a P3O&like shape, whereas the average of “low” EHF trials (below

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median EHF) did not. This underlines the functional role of delta responses for the P300 wave. 2. P300-like responses to NON-TARGET stimuli: From a common ensemble of TARGET and NON-TARGET responses, the single trials with highest EHF values were selected and averaged. The resulting ERP is almost congruent with the average of TARGET responses only. Thus it may be possible to extract single trials with P300 responses to NON-TARGETS [cf. Demiralp et al. in press]. The slow positive wave in TARGET responses belongs to the P300-waves which are widely accepted to be related to task-relevant cognitive processes. In summary, single-trial analysis of the P300-delta response hints at psychophysiological roles of event-related delta oscillations.

SYMPOSIUM 5A: Working Memory and Delayed Reactions in Normal and Pathological Conditions Part I-In part sponsored by Pfizer 31 NEUROELECTRIC SIGNALS OF WORKING MORY PREDICT IQ TEST SCORES

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Alan Gevins, Michael E. Smith and Georgia Rush SAM Technology and EEG Systems Laboratory, 101 Spear St., Suite #203, San Francisco, CA, 94105, USA Current theories of cognition prescribe a close relationship between working memory ability and general intelligence. In recent high-resolution EEG studies, we found that increasing working memory load in an n-back style working memory task affects a variety of EEG spectral features (Gevins, Smith, McEvoy, and Yu, 1997, Cerebral Cortex, 7, 374-385) and evoked potential components (Gevins, Smith, et al., 1996, Electroencephalogr. Clin. Neurophysiol., 98, 327-348). To test the hypothesis that these neural signals of working memory relate to general intelligence, a sample of sixty ethnically diverse and gender matched young adults with average to superior scores on a standard intelligence test (WAIS-R) performed working memory tasks concurrent with EEG recordings. Reaction times were negatively correlated with test scores. The amplitude and reactivity of an EEG spectral feature in the theta band from frontomesial cortex were positively correlated with test scores, as were signals in the lower portion of the alpha band. The peak latency of the P3 evoked potential associated with stimulus categorization was negatively correlated with test scores, with a weaker positive relation between P3 amplitude and test scores. Combinations of working memory task behavioral and neuroelectric variables predicted intelligence test scores with a high degree of accuracy (multiple r > 0.8). The results demonstrate a close relationship between the neural processes used to maintain representations in working memory and scores obtained on a standard psychometric test of intelligence. The results provide no evidence for any relationship between these variables and

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gender or ethnic@. Supported by the U.S. Air Force Office of Scientific Research.

32 VISUAL, VISUOMOTOR TRANSFER AND PREFRONTAL EXECUTIVE TIMES IN VERBAL REACTIONS R.Q. Cracco, V.E. Amassian, P.J. Maccabee and J.B. Cracco State University of New York Health Science Center at Brooklyn, USA Transcranial Magnetic Stimulation @MS) of cerebral cortex is associated with both excitatory and inhibitory properties which make it possible to trace interconnections between cortical areas. TMS has superior temporal resolution but inferior spatial resolution compared with functional MRI. Here we describe experiments using TMS to trace the flow of symbolic visual information from retina to calcarine cortex to frontal lobe to voice production. In an alert individual, the latency to initial vocalization of a visually presented symbol is about 350 ms. Investigations with TMS show that this time consists of the retinal-calcarine cortex transfer time (approximately 60 ms), relay of the symbolic representation out of calcarine cortex (120 ms), its arrival in and facilitation of frontal cortex (120-140 ms), frontal lobe activation of laryngeal EMG (6-20 ms) and initiation of voice (80 ms). There remains about 125 ms (350 -(130 + 15 + SO) which includes time for perception of the visual symbol and for the visual representation in frontal cortex to be coded into appropriate motor output for language.

33 EVENT-RELATED BRAIN ACTIVITY COLOR-WORD MATCHING TEST

DURING

G. Comi’, L. Leocani’s’, V. Martinelli’ ‘Clinical Neurophysiology, H.S. Raffacle, University of Milan, Italy *Neurology, H.S. Raffacle, University of Milan, Italy The Stroop color-word matching task is a test used for the assessment of frontal executive functions. Cognitive impairment is one of the most frequent complications of Multiple Sclerosis (MS), particularly related to frontal executive functions, mostly reflecting a subcortical dementia. We selected 11 right-handed MS patients, who failed in three or more tests evaluating frontal functions, among an extensive neuropsychological battery. These patients were compared with 10 righthanded MS patients matched for age, disease duration and disability, who did not fail at any test. EEG was recorded while patients performed self-paced movements of the right thumb and during mental performance of the Stroop test. Manual reaction time to the Stroop test was also measured. Reaction time during the Stroop test was significantly slower

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in patients with frontal cognitive impairment compared to the unaffected patients. The main components of the event-related potentials to the Stroop stimuli were modified both in latency and amplitude in patients with frontal cognitive impairment. Moreover, in this group, the movement-related EEG potential preceding and during movement execution was significantly reduced over the fronto-central regions contalateral to the movement. These data suggest that frontal cognitive involvement in MS corresponds to a reduced bioelectrical activity not only in relation to mental performance of a task evaluating executive functions, but also during a self-paced movemen paradigm.

34 TASK-INDEPENDENT VERBAL REACTIONS

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P. Pinclli Department of Neurology, “S. Maugeri” Foundation, IRCCA, Medical Centre of Rehabilitalion, Veruno (ENO), Italy Methodologies such as Multiple Delayed Reaction Verbochronometry (MDRV) allow us to identify early cerebral impairments in the different phases of brain cognitive functions: (1) programming, (2) working memory task-indepedent and task-dependence processes, (3) transfers between perceptive and executive systems, and (4) modulation of the final output via intermediary feedbacks of correction in the ongoing processes of behavioral control. The time elapsing between the appearance of the task-stimulus and the go-signal in delayed reactions is associated with a recurrent activity in the internal circuit formed by prefrontal (dorsolateral) and subcortical neural assemblies. This flow of programming impulses ends at the onset of the executive processes and corresponds to the so-called immediate memov or purpousefil attention. With MDRV we have detected an impairment of delayed reactions at the module-independent, task-independent, abstract level (and therefore independent of the specific task, i.e. the word). Such impairment is related to the condition of hypofrontality that is typical for schizophrenia, and it is revealed by the loss of the facilitatoty process that is exerted on the threshold of the executive systems during the foreperiod between the task-stimulus and the go-signal. In fact the latency time of delayed reactions in these patients is equal or longer than that of the immediate rections. The same results have been obtained with reactions to stimuli requiring manual or oculomotor performances. In MDRV the subject is requested to perform delayed reactions with a foreperiod shorter than the duration of the ongoing internal reveberating circuits, ie, < 0.4 s. In this way we can test lateral inhibitory processes. In the classic delayed reaction the task-stimulus is present during the whole foreperiod on the screen of the monitor. On the other hand a more adequate investigation to study memory (STM) impairments associated with laterodorsal tem-