Prefrontal modulation of visual processing in humans.

Single neuron, evoked potential and metabolic techniques show that attention influences visual processing in extrastriate cortex. We provide anatomical, electrophysiological and behavioral evidence that prefrontal cortex regulates neuronal activity in extrastriate cortex during visual discrimination. Event-related potentials (ERPs) were recorded during a visual detection task in patients with damage in dorsolateral prefrontal cortex. Prefrontal damage reduced neuronal activity in extrastriate cortex of the lesioned hemisphere. These electrophysiological abnormalities, beginning 125 ms after stimulation and lasting for another 500 ms, were accompanied by behavioral deficits in detection ability in the contralesional hemifield. The results provide evidence for intrahemispheric prefrontal modulation of visual processing.

Predictive value of novel stimuli modifies visual event-related potentials and behavior.

OBJECTIVE: We examined how behavioral context influences novelty processing by varying the degree that a novel event predicted the occurrence of a subsequent target stimulus. METHODS: Visual event-related potentials (ERPs) and reaction times (RTs) were recorded in 3 detection experiments (23 subjects). The predictive value of a novel stimulus on the occurrence of a subsequent target was varied as was novel-target pairing intervals (200-900 ms). In Experiment 1, novel stimuli always preceded a target, in Experiment 2, 40% of novel stimuli were followed by a target, and in Experiment 3, novel stimuli occurred randomly. RESULTS: In Experiment 1, RTs following 100% predictive novels were shortened for targets at all spatial locations and novel-target pairing intervals. Novel stimuli predicting a target generated a central negativity peaking at 300 ms and reduced P3a and P3b ERPs. In Experiments 2 and 3, target RTs were prolonged only when novel and target stimuli were presented in the same spatial location at short ISIs (200 ms). The central novel N2 was smaller in amplitude in comparison to Experiment 1, and novelty P3a and target extrastriate N2 and posterior scalp P3b ERPs were enhanced. CONCLUSIONS: The enhanced N2 for 100% predictive novel stimuli appears to index an alerting system facilitating behavioral detection. The same novel stimuli with no predictive value distract attention and generate a different ERP pattern characterized by increased novelty P3a and target P3b responses. The results indicate that behavioral context determines how novel stimuli are processed and influence behavior.

[The effect of cigarettes on somatosensory potentials]. / Efectos del cigarrillo sobre los potenciales somatosensoriales.

INTRODUCTION AND OBJECTIVE: The physiological and pathological effects of cigarettes on the nervous system have been widely studied, but none of the investigations carried out has enabled us to determine the degree to which nicotine may affect the central pathways of somatosensorial evoked potentials in humans. MATERIAL AND METHODS: Following parameters established internationally for investigation of the effects of nicotine on the nervous system, we find that the N18 wave obtained by stimulation of the median nerve before smoking completely disappears after smoking for 3 minutes and reappears 10 minutes after smoking has stopped. CONCLUSIONS: Therefore, we conclude that the action of nicotine on these evoked potentials is mainly subcortical, and for this reason it is essential to investigate the toxicological history before carrying out any clinical or neurophysiological study, since this might affect the results obtained.

Estimate of physiological variability of peak latency in single sweep P300.

Among single sweep records of event-related potentials (ERPs), the peak latency of P300, which is one of the most prominent positive peaks in the ERP obtained in the oddball paradigm, may vary depending on the conditions of the subject. In the analysis of characteristics of the variability in the peak latency, it is important to know to what extent the variability of the measured peak latency (measured variability) is actually caused by physiological factors (physiological variability). In our previous study, a method was developed for judging whether the physiological variability really exists or not, and if it does exist, the developed method extracts the physiological variability from the measured variability based on a limited number of single sweep records. In the present study, based on the P300 waveforms which were detected by blinded visual inspection of the ERP data obtained by an auditory oddball paradigm from 12 healthy adults, the physiological variability was shown to exist with a confidence level of 95% for all subjects. Furthermore, its interval estimate was calculated by subtracting noise variability from the measured variability with a confidence level of 80%, and it was found to range from 17 to 57 ms for all subjects.

The effects of tobacco smoking on the short, middle, and long latency responses of the blink reflex in humans.

The three responses (R1, R2, and R3) of the electrically elicited blink reflex (BR) obtained in four normal human subjects were investigated before and after smoking both a filtered and an unfiltered cigarette. The changes observed in the BR were stronger and statistically more significant for the unfiltered than for the filtered cigarette, (p < 0.0001) and were more dramatic in R3 than R1 or R2. The action of nicotine on central pathways located at the interneuronal network of the brainstem, basal ganglia, and C fiber structures involved with this reflex seems to be the most likely mechanism for these findings.

P300 abnormalities in patients with selective impairment of recent memory.

We recorded auditory event-related potential (ERP) by using the standard oddball paradigm in seven amnestic patients. Patients were divided into three groups according to brain CT or MRI findings. (1) Three patients with no detectable lesion, including two patients studied during the episode of transient global amnesia, showed a well-defined P300. (2) Three patients with detectable lesions in the mesial temporal lobes did not show any wave form corresponding to P300. In two of these three patients, the ERP wave form showed a significant change in accordance with the improvement of MRI findings. (3) One patient who had a hypothalamic lesion due to total resection of craniopharyngioma showed a low-amplitude P300. Although neuropsychological examinations showed selective and severe impairment of recent memory function in all of these patients, no significant relationship was found between the degree of memory disturbance and P300 abnormality. These results suggest that P300 is more affected by existence and extension of brain lesions, especially in the mesial temporal lobes, rather than degree of memory disturbance. However, these results do not necessarily suggest that the potential generated in the mesial temporal lobes is directly recorded as a component of the scalp-recorded P300.

Construction of a morphological filter for detecting an event-related potential P300 in single sweep EEG record in children.

A morphological filter for single sweep records of event-related potential (ERP) obtained in an auditory oddball paradigm, especially P300 waveform, was constructed. By combining four basic operations; erosion, dilation, opening and closing, we could derive a desired filter whose properties fit the current objectives. The morphological filter for the single sweep records of ERP was constructed by taking into account the features of the signal and noise components. The morphological filter had superior properties for distinguishing the signal from the noise even when both were within the same frequency band, as in case of children. The constructed morphological filter was evaluated by using the simulation data of ERP and then applied to the actual ERP data obtained from nine normal children. The constructed morphological filter was proved to be an appropriate tool for single sweep analysis of ERP.

Clinical neurophysiological comparative study on HTLV-1 associated myelopathy/tropical spastic paraparesis.

In order to determine the neurophysiological characteristics of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) throughout the world, we analyzed and compared the most common clinical neurophysiological studies (CNPS) performed in this entity from those places with a high prevalence and interesting regional differences were noted. African patients showed a noteworthy involvement of the peripheral nervous system (PNS). Chilean patients displayed a more circumscribed abnormality around the spinal cord. The migrants from the West Indies to England showed important visual, and somatosensory evoked potential (SSEP) alterations in the upper limbs (UL). Japanese patients also presented some involvement of the PNS, but their illness duration was less protracted than that observed in other countries. The differences found in visual pathways and PNS involvement among these groups were statistically significant (p < 0.05). Thus, this study shows not only a widespread subclinical involvement in both central and PNS in HAM/TSP, but also strongly supports the idea that the lesion distribution and progression of this disease are different among countries. Such differences could likely be due to the action of the so-called environmental co-factors present in each of these areas which should be promptly investigated.

Automatic detection method of P300 waveform in the single sweep records by using a neural network.

Event-related potentials (ERPs) are responses related to the recognition of certain stimuli. P300 is the most important positive component in the ERP and appears around 300 ms after the target stimulus in the oddball paradigm. In our previous work, we proposed a method for the automatic detection of the P300 waveform in single-sweep records by using a correlation technique. However, determination of the threshold values of the P300 waveform for the correlation study was not an easy task. In skirting this problem, we developed an automatic method of detecting a single-sweep P300 waveform by using an artificial neural network. We selected appropriate characteristic parameters of positive peaks as input signals for the input layer units, and the weights between the layers were determined by using the back-propagation algorithm. The neural network for P300 detection was obtained automatically, based on the data of ERPs obtained from 11 healthy males, and gave substantial accuracy for P300 detection. Furthermore, by using this neural network we clarified the way in which the P300 waveform is judged visually by each inspector.

Characteristics of auditory P300 in children: application of single trial analysis.

As, especially in children, cognitive function might vary from one stimulus to the other, even when the same target stimuli are presented in the oddball paradigm, we applied the single trial analysis adopting discrete Fourier transformation followed by inverse discrete Fourier transformation to the auditory P300 for the first time in children. In 9 children, age 9-13 years, a positive peak was clearly identified in approximately a quarter of the processed single sweep responses to target stimuli (single sweep P300), whereas it was observed less frequently for non-target stimuli. In 2 children of age 6 years, it was difficult to discriminate single sweep P300 from background EEG activities even in the processed data. As for the former group, the detection ratio of P300 in single sweep target responses ranged from 10.0 to 40.0%, and its mean latency and amplitude ranged from 311 to 348 ms and from 31.7 to 41.5 microV, respectively. There was a significant correlation between average data and single sweep data in terms of the P300 latency. However, the amplitude of P300 in the average data bore no relation to the detection ratio, mean amplitude or variability of latency among single sweep P300s. As compared with adult data previously reported, the detection ratio of single sweep P300 was lower and the P300 amplitude was higher in childhood. P300 in children, at least past puberty, can be analyzed by using the single trial method, which is expected to provide more information about the development of human higher brain functions, especially cognitive function.

Automatic detection of P300 in single sweep records of auditory event-related potential.

In the conventional recording of event-related potentials (ERPs) by the "oddball" paradigm, the subject may employ different strategies for processing one stimulus from the other even within the same session because of variable psychological state. Hence, "averaging" may not necessarily be suitable for recording ERP. We have therefore established a method for single trial recording of auditory ERPs by processing the EEG data through discrete Fourier transform followed by inverse discrete Fourier transform with the low pass filter of 8 Hz (digital filter). Each single sweep response of the processed data was visually evaluated as to whether it contained P300 or not by three investigators who were made completely blind with respect to the category of each response. As the result, a positive peak at a latency of 200-500 ms was recognized in the single sweep responses to target stimuli at a significantly greater frequency (40-60%) than in those to nontarget stimuli (0-18%). Then a new method for the automatic detection of P300 was established based on the data of 11 subjects belonging to the training group, by taking into account, in addition to the correlation coefficient analysis in which the template was computed specifically for each subject, other criteria with respect to the amplitude and waveforms, so that a good agreement with the results of visual inspection as to the presence or absence of P300 could be achieved for both target and nontarget responses. This automatic analysis method was successfully applied to five other subjects of the test group. The peak latency and amplitude of the detected positive peaks significantly varied among single target responses even within the same session. The reaction time significantly correlated positively with the peak latency of the detected positive peaks and negatively with the amplitude of those peaks, supporting the usefulness of the present method.

Both primary motor cortex and supplementary motor area play an important role in complex finger movement.

In order to clarify the roles played by the primary motor cortex and the supplementary motor area in the execution of complex sequential and simple repetitive finger movements, regional cerebral blood flow (rCBF) was measured with PET using 15O-labelled water in five normal subjects. The PET data of each individual subject co-registered to his own MRI, was analysed. Compared with the resting condition, the mean rCBF was markedly increased in the contralateral sensorimotor cortex (M1-S1) and moderately increased in the contralateral cingulate gyrus and putamen in both the simple and complex motor tasks. During the complex motor task, in addition to the above, the mean rCBF was markedly increased in the supplementary motor area and the contralateral premotor area, and moderately increased in the ipsilateral M1-S1 and cerebellum. In the supplementary motor area, there was a moderate rCBF increase also during the simple task. However, comparison of the mean rCBF increase against the resting condition between the two tasks revealed a greater increase during the complex task than in the other only in the supplementary motor area and the ipsilateral M1-S1. Thus, in agreement with our previous electrophysiological findings, not only the supplementary motor area but also the M1-S1 seems to play an important role in the execution of complex sequential finger movements.

Auditory event-related potentials in patients with systemic lupus erythematosus.

We studied auditory event-related potentials (ERPs) in 17 patients with systemic lupus erythematosus (SLE). Latencies of N100 and P200 components were normal in all patients, whereas the latencies of target P300 and nontarget P300 components were significantly prolonged in SLE patients with and without cognitive dysfunction. The P300 component of ERPs can be applied to evaluate the cognitive aspects of central nervous system manifestations in SLE patients.

Current source density mapping of somatosensory evoked responses following median and tibial nerve stimulation.

Potential recording of brain activities always encounters the problem resulting from the activation of reference electrodes. Current source density (CSD) computation does not take reference sites into account and consequently may better localize the generator sources. In the past, several attempts have been made to record CSDs of the somatosensory evoked responses (SERs) following median nerve stimulation. In order to compare the generating mechanisms of SERs following median nerve and tibial nerve stimulation, the scalp CSD distributions of the median nerve SER and the tibial nerve SER were compared in 5 normal subjects. In the median nerve SER, far-field potentials such as P14 and N16 were abolished in the CSD records. N20, P25 and N35 showed almost identical CSD distributions, albeit P25 had a reversed polarity. By contrast, the tibial nerve SER showed similar distributions for P40 and P60 CSDs, but N50 had a different distribution from the others. In the potential records, P40 and P60 were distributed predominantly ipsilateral to the stimulus (paradoxical lateralization), whereas the P40 and P60 CSDs formed a dipole localized over the contralateral foot somatosensory area. N50 disclosed the same tendency, although it had a slightly different CSD pattern from that of P40 and P60. These findings suggest that the median nerve and tibial nerve SER components are not necessarily comparable and that under certain circumstances CSDs are better indicators of local electrical events than the corresponding potentials.