The early component of the visual evoked magnetic field

Several EEG studies have reported an early component of the visual evoked potential. However, it is controversial whether this component is cortical or subcortical. Our study has aimed to clarify this problem using MEG and EEG in nine normal volunteers. A total of 4000 stimuli were presented to the monocular visual hemifield through a light-proof stimulating goggle and the visual evoked magnetic field and visual evoked potential was measured above the occipital lobe. The early component was observed in three of the nine subjects. The latency ranged from 40 to 45 ms in MEG and from 39 to 47 ms in EEG. The result of dipole localization analysis showed that its origin was cortical, and specifically, the striate cortex.     

Discriminative power of visual evoked potential characteristics in multiple sclerosis

To investigate the discriminative power of pattern-reversal visual evoked potential characteristics (peak latencies and amplitude) and to test whether the addition of visual evoked potential amplitude can increase the power of the visual evoked potential in the diagnosis of multiple sclerosis, we retrospectively studied visual evoked potentials in 59 patients with definite multiple sclerosis and 126 control subjects. Two check sizes (17' and 10') were used. Females had significantly higher amplitudes and shorter latencies than males. N80 latency showed a gradual increase and P100 amplitude a decrease with age. P100 latency was stable between the ages of 20 and 55 years but was increased in childhood and the elderly. The significance of visual evoked potential peak latencies and amplitude in separating the two groups was investigated by means of a (multivariate) discriminant analysis. The visual evoked potential with a pattern of 10' could be measured in 58% of patients with multiple sclerosis. The exclusive use of the P100 amplitude in the discriminant analysis resulted in a percentage of correctly classified cases of 84%, whereas for P100 and N80 latency it was 85% and 90%, respectively. With the 17' pattern, the N80 latency yielded also a higher correct percentage than did the P100 latency. Although N80 latency is, to a greater extent than P100 latency, influenced by age, sex and size of stimulus pattern, when these influences are accounted for, the N80 latency is a more sensitive measure than P100 latency in the classification of multiple sclerosis. Combined use of latency and amplitude for discriminant analysis yielded no significant improvement of the percentage of correctly classified cases.     

Reliability of the peroneal latency in normal ankles

The aim of this study was to determine the reliability of peroneal latency between trials and to compare the right and left sides in healthy subjects. A dual platform trapdoor was constructed to tilt the right or the left ankle by 30 degrees in the frontal plane. Electromyography recorded the onset of peroneal activity in response to this perturbation, and an accelerometer detected the onset of trapdoor movement. Peroneal latency was determined algorithmically as the time difference between the onset of trapdoor movement and the onset of peroneal activity. Twenty trials were recorded from 31 right leg dominant, healthy subjects. Peroneal latency was measured successfully for 613 trials (99% success rate). A repeated measures analysis of variance showed a main effect for side with the right, dominant side recording a longer latency. Intertrial reliability of the peroneal latency was high (intraclass correlation coefficients for the right and left legs were .91 and .82, respectively). Thus, peroneal latency is a reliable measure of the polysynaptic reflex ares involved in the response of these muscles to a sudden inversion stress.     

Recognition potential: sensitivity to visual field stimulated

The recognition potential (RP) was distinguished from P3 and eye blink responses by its sensitivity to visual area stimulated. Images were flashed in upper and lower hemifields. Current source density profiles were computed, using 16 midline scalp electrodes. For P3 and eye blink profiles, the hemifield stimulated was not a significant factor. For the recognition potential, upper and lower field stimulation produced radically different profiles. An improved recognition potential signal was obtained by a new mathematical procedure. It used the difference in sensitivity to visual area stimulated to reject P3 and eye blink responses.     

A new method to determine pudendal nerve motor latency and central motor conduction time to the external anal sphincter

By placing the earth electrode between the site of the stimulus and the site of derivation, peripheral motor latency to the external anal sphincter can be determined and thus central motor conduction time (CMCT) can be calculated. In 18 volunteers we found a total motor conduction time of 19.4 msec (S.D. 1.71) after stimulation of the motor cortex and recording above the external anal sphincter. Latency was 5.6 msec (S.D. 0.66) when stimulated above L1 and pudendal latency (MEPuL) after stimulation above S3 was 2.5 msec (S.D. 0.32). CMCT to L1 (TMCT minus MCT to L1) was 13.8 msec (S.D. 1.13) and to S3 (TMCT minus MEPuL) it was 16.9 msec (S.D. 1.67). This method allows us to locate spinal dysfunction more precisely and also improves diagnosis of a possible neuropathy of the pudendal nerve.     

Compensation for gaze perturbation during inactivation of the caudal fastigial nucleus in the head-unrestrained cat

Muscimol injection in the caudal part of the fastigial nucleus (cFN) leads, in the head-unrestrained cat, to a characteristic dysmetria of saccadic gaze shifts toward visual targets. The goal of the current study was to test whether this pharmacological cFN inactivation impaired the ability to compensate for unexpected perturbations in gaze position during the latency period of the saccadic response. Such perturbations consisted of moving gaze away from the target by a transient electrical microstimulation in the deep layers of the superior colliculus simultaneously with extinction of the visual target. After injection of muscimol in the cFN, targets located in the contralesional hemifield elicited gaze shifts that fell short of the target in both "perturbed" and "unperturbed" trials. The amplitude of the compensatory contraversive gaze shifts in perturbed trials coincided with the predicted amplitude of unperturbed responses starting from the same position. Targets located in the opposite hemifield elicited hypermetric gaze shifts in both trial types, and the error of compensatory responses was not statistically different from that of unperturbed gaze shifts. These results indicate that inactivation of the cFN does not interfere with the ability of the head-unrestrained cat to compensate for ipsiversive or contraversive perturbations in gaze position. Thus the gaze-related feedback signals that are used to compute a reference signal of desired gaze displacement are not impaired by cFN inactivation.     

Chronic electrical stimulation of the facial nerve causes signs of facial nucleus hyperactivity

The proximal segment of the facial nerve in rats was stimulated electrically daily for a duration of 2-10 min. After 4-8 weeks of such stimulation, 12 of 18 rats developed abnormal muscle responses that could be demonstrated by recording the electromyographic response from lower face muscles (the mentalis muscle) while the temporal branch of the facial nerve was being stimulated electrically. This abnormal electromyographic response consists of activity that appears in the latency range 6.5-15 ms. In addition, these chronically stimulated rats developed signs of facial synkinesis on the side that had been chronically stimulated. This could be demonstrated by recording electromyographic activity when the blink reflex was being elicited by electrical stimulation of the ophthalmic nerve. Rats in which electrodes had been implanted but which had not been stimulated did not develop any abnormal electromyographic activity. The abnormal electromyographic activity that could be recorded in rats that had been stimulated chronically could not be recorded 4-8 weeks after the stimulation had been terminated. We interpret these results to indicate that chronic electrical stimulation of the facial nerve can render the facial motonucleus hyperactive, and that the signs of this hyperactivity (abnormal muscle response and synkinesis) are similar to those typically seen in patients with hemifacial spasm. We thus presume that these results support the hypothesis that it is the irritation of the facial nerve from a compressing blood vessel that causes the facial nucleus to become hyperactive in patients with hemifacial spasm.     

Prolongation of conduction time during premature stimulation in the human atrium is primarily caused by local stimulus response latency

BACKGROUND: Conventional clinical electrophysiological techniques cannot accurately differentiate between local stimulus response latency and propagation time of the atrial response. The purpose of this study was to identify and distinguish local stimulus response latency from impulse propagation time in the human right atrium during programmed electrical stimulation. METHODS: Pacing was performed from two atrial sites (high and low right atrium) in 19 patients, using monophasic action potential recording/pacing combination catheters (interelectrode distance < 2 mm). Local stimulus response latency (interval between stimulus artifact and upstroke of the local monophasic action potential), and propagation time (interval between local and remote monophasic action potential upstroke) were evaluated at a basic cycle length (S1-S1) of 600 ms and as a function of the extrastimulus proximity (interval between extrastimulus and effective refractory period). Data are presented as means +/- SEM. RESULTS: During basic stimulation, local latency was very small (3.8 +/- 1.7 ms). During premature extrastimulation (proximity < 70 ms), local latency increased progressively with decreasing coupling intervals. Prolongation of local latency was most pronounced during stimulation close to the effective refractory period with local stimulus response latency increasing to 18.3 +/- 1.4 ms (380 +/- 7.9%) at 10 ms proximity (P < 0.002) and to 27.9 +/- 3.7 ms (630 +/- 13.2%) at 5 ms proximity, respectively (P < 0.0001). The impulse propagation time between the stimulation site and the remote recording site was on average 54.5 +/- 14.3 ms during basic stimulation, and increased up to 62.1 +/- 13.5 ms (14.0 +/- 8.4%), which was not significant. CONCLUSIONS: The intra-atrial impulse propagation remained essentially unchanged during the entire range of premature stimulation. Local stimulus response latency was negligible and constant during late coupling intervals but increased dramatically when extrastimulation approached the preceding repolarization phase. This has the following clinical impact: first, local stimulus response latency during premature extrastimulation curbs the targeted atrial response interval second, local stimulus response latency, not propagation time, seems responsible for the greater functional than effective refractory period during electrical stimulation; third, local stimulus response latency should be considered in pace mapping for accurate comparison of conduction time before pacing with that during pacing.     

A dynamic and quantitative study of pattern visual evoked potentials and gamma-aminobutyric acid neurones in the lateral geniculate nucleus and the visual cortex of monocular deprivation cats

PURPOSE: To assess the effects of monocular lid closure during critical period on cortical activity. METHOD: Pattern visual evoked potentials (PVEP) of the normal and the monocular deprivation (MD) cats were dynamically measured and the number of gammaaminobutyric acid immunopositive (GABA-IP) neurones of the area 17 of the visual cortex and the lateral geniculate nucleus (LGN) was quantitatively compared by using immunohistochemical method (ABC). RESULTS: The amplitude of the N1-P1 attenuated in deprived eyes (DE), NE/DE at postnatal week (PNW) 7-8 (P < 0.05), NE/DE at PNW 15-16 (P < 0.01); while P1 latency delayed, NE/DE at PNW 7-8 (P > 0.05), NE/DE at PNW 15-16 (P< 0.05). The numbers of GABA-IP neurones in layer A1 of the ipsilateral LGN and in layer A of the contralateral LGN, compared to those in the corresponding normal laminae, were not significant at PNW 7-8 and PNW 11-12 (P > 0.05), while in the same cats a reduction in the number of GABA-IP neurones was found in layer IV of area 17 at PNW 11-12 (P < 0.05). However, with longer survival of 3-4 weeks in duration, the numbers of GABA-IP neurones in the deprived laminae of LGN were remarkably reduced (P < 0.05). CONCLUSIONS: The amplitude of N1-P1 components is sensitive to the effects of monocular deprivation. Monocular deprivation in cats during critical period leads to dramatic changes of the number of GABA-IP neurones in the LGN and cortical layer IV receiving inputs from the deprived eye in cats. The deprivation-induced reduction in GABA-IP neurones is delayed in the LGN compared with the visual cortex. PVEP of the MD cats is consistent with the damage of its GABA system in visual cortex.     

Reduced frequency of knowledge of results enhances motor skill learning.

Relative frequency of knowledge of results (KR) is the proportion of KR presentations to the total number of practice trials. Three experiments are reported in which the effects of variations in acquisition KR relative frequency were examined. Experiment 1 showed that a markedly reduced KR relative frequency during practice was as effective for learning as measured by various retention tests, compared with a 100% KR practice condition. In Experiments 2 and 3, when the scheduling of KR was manipulated so that the number of KR trials was systematically lowered across practice, a reduced average relative frequency enhanced learning as measured by a delayed no-KR retention test (Experiment 2) and a retention test in which KR was provided (Experiment 3). Results are inconsistent with predictions from an acquisition-test specificity hypothesis and conventional motor learning theories and thus suggest a revision in the principles governing the role of KR for motor learning. Empirical support is provided for the KR guidance hypothesis (A. W. Salmoni et al; see record 1984-22348-001) and for various encoding-retrieval operations associated with spaced retrieval practice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fixation conditions, the foveola and saccadic latency

Saccades are often elicited in the laboratory by the abrupt step-displacement of a single lit point which is initially the foveolar fixation point and then the eccentric refixation target. This was our Control condition. Four experiments modified the fixation arrangements to examine the effect of altered foveolar stimulation on saccadic latency and accuracy to targets within the central +/- 6 deg of the visual field. (1) No foveolar fixation point: The subject fixated the empty space midway between a pair of fixation guides, which later collapsed into a single refixation target. Latencies for small saccades were similar to the Control values. (2) No foveolar fixation point and no real refixation target: A pair of fixation guides underwent a yoked displacement, and it was easy to fixate and track the invisible midpoint. The smallest saccades were hypermetric, and the typical pattern of latency variation with retinal eccentricity was exaggerated in scale. (3) Spatial effects of a persistent non-target: The precise position of a non-target was important, latency increases being in the ipsilateral hemifield when the non-target was intrafoveolar and unilateral, bilateral when intrafoveolar and on the midline, and local when the non-target was extrafoveolar. (4) Temporal effects of a foveolar fixation point: Blanking an otherwise persistent fixation point for as little as 1 msec at the time of target presentation reduced the expected latency increase. We conclude that the position and timing of foveolar illumination can be critical for saccades of all sizes.     

Odor-induced currents in Xenopus olfactory receptor cells measured with perforated-patch recording

1. Odor-evoked currents were recorded in Xenopus laevis olfactory receptor neurons (ORNs) by the use of conventional, as well as nystatin and gramicidin-perforated, whole cell recording. The odor-evoked current ran down quickly in conventional, but not in perforated, whole cell recording. All three types of recording gave similar values for the amplitude, latency, time-to-peak, recovery time, and reversal potential of the odor-evoked current. 2. A secondary Cl current comprised a significant part of the odor-evoked current (55-65%). ECl measured by gramicidin perforation, which does not alter [Cl-]i, was -2.3 +/- 5.0 (SE) mV, indicating that these neurons maintain a high [Cl-]i and that the secondary Cl current plays an excitatory role in olfactory transduction.     

Mnemonic responses of single units recorded from monkey inferotemporal cortex, accessed via transcommissural versus direct pathways: a dissociation between unit activity and behavior

Three macaques were trained on a task in which a sequence of single visual images was presented serially, and the monkeys signaled whether the image was a new or a repeated one. The optic chiasm and splenium of the corpus callosum were transected, leaving the anterior commissure as the only path for cortical interhemispheric transfer. Images were presented to only one eye at a time. Re-presentations of images to the same eye were recognized correctly in >95% of trials. A robust stimulus-specific adaptation (i.e., a reduced response to a repeated image) was seen in the population of single units recorded from inferotemporal cortex during these same trials. When an interhemispheric transfer was demanded of the animals (i.e., the re-presentation was made to the other eye), recognition performance was somewhat reduced, to 86% correct. Interestingly, in this situation the stimulus-specific adaptation disappeared completely. The disappearance occurred regardless of whether the transfer direction was from the hemisphere ipsilateral to the recording site to the hemisphere contralateral to the recording site, or vice versa. Thus, stimulus-specific adaptation in inferotemporal cortex units is not required for recognition.     

Latent inhibition in the conditioned electrodermal response.

Measured the effects of preexposure to the CS, amount of pre-exposure, and delay between pre-exposure and conditioning in a classical electrodermal conditioning experiment with 139 female nursing students. 3 conditions were investigated: no delay, 1-hr delay, and 24-hr delay. In each of these delay conditions Ss were pre-exposed to either 100 or 50 presentations of the to-be-conditioned stimulus or 100 or 50 presentations of an irrelevant stimulus. Results were analyzed separately for long and short latency responses in terms of amplitude, magnitude, latency, recruitment, and frequency. It was found that CS pre-exposure reduced the frequency of responding regardless of delay or number of pre-exposures. There was a significant CS Pre-exposure main effect for short latency responses and a significant Trial Blocks * CS Pre-exposure interaction effect for long latency responses. Theoretical and methodological implications are discussed. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Health administration functions in occupational health

Study of optimum seeking method with orthogonal test for auditory P300 measuring was carried out in healthy adolescents. The result showed that the optimal conbination of parameters was as follows: stimulus sound was Logon, recording electrode site Cz, analysis time 750 ms, average 100, stimulus rate 1 c/s, target stimulus (TS) probability 10%, bandpass filter 1-50 Hz, non-target stimulus (NTS) freqency 1 kHz, target stimulus (TS) frequency 2 kHz, stimuli intensities 110 dB peSPL. The normal values of auditory P300, obtained from 30 healthy adolescents, including latencies and amplitudes, were measured under optimal parameters. P300 latency was about 310 ms, RT about 258 ms, these two values present a significant linear correlation.     

Sustained visual-spatial attention produces costs and benefits in response time and evoked neural activity

This study investigated the simple reaction time (RT) and event-related potential (ERP) correlates of biasing attention towards a location in the visual field. RTs and ERPs were recorded to stimuli flashed randomly and with equal probability to the left and right visual hemifields in the three blocked, covert attention conditions: (i) attention divided equally to left and right hemifield locations; (ii) attention biased towards the left location; or (iii) attention biased towards the right location. Attention was biased towards left or right by instructions to the subjects, and responses were required to all stimuli. Relative to the divided attention condition, RTs were significantly faster for targets occurring where more attention was allocated (benefits), and slower to targets where less attention was allocated (costs). The early P1 (100-140 msec) component over the lateral occipital scalp regions showed attentional benefits. There were no amplitude modulations of the occipital N1 (125-180 msec) component with attention. Between 200 and 500 msec latency, a late positive deflection (LPD) showed both attentional costs and benefits. The behavioral findings show that when sufficiently induced to bias attention, human observers demonstrate RT benefits as well as costs. The corresponding P1 benefits suggest that the RT benefits of spatial attention may arise as the result of modulations of visual information processing in the extrastriate visual cortex.     

The modulation of somatosensory evoked potentials during the foreperiod of a forewarned reaction time task

During the foreperiod of a forewarned reaction time (RT) task reflexes in the executing limb increase to a lesser extent than those in the contralateral limb. This is possibly due to input modulation. The present study investigates the possibility of cutaneous sensory modulation during motor preparation by studying the amplitudes of somatosensory evoked potentials (SEPs). Eighteen subjects performed a forewarned RT task with the same fingers as the ones which were electrically stimulated. SEPs evoked during the 4 sec preparatory period were compared to those evoked during movement execution and during the resting period after the motor response respectively. During response execution most SEP components showed smaller amplitudes, i.e., they were gated, which agrees with other studies. In the first part of the foreperiod no SEP modulation was observed. Towards the end of the foreperiod, 500 msec before the response stimulus (RS), the amplitude of the contralateral parietal N70-P100 was significantly decreased, while the P45-N70 showed a similar tendency. However, at the same time the P100-N140 was increased in amplitude. The decrease of the intermediate latency components towards the end of the foreperiod is discussed in terms of gating, while the increase in the long latency component is discussed with respect to a decrease in RT on trials where the fingers were stimulated just before the RS, pointing to the role of attentional mechanisms.     

Carcinoid disease: review of the literature

A novel method is described for assessing drug bioavailability from pharmacologic data. The method is based upon a generalized model for the relationship between the observed effect (E) and the input rate (f): E = phi (ce delta * f), where * denotes convolution, ce delta is effect site unit impulse response ("amount" of drug at the effect site resulting from the instantaneous input of a unit amount of drug) and phi is transduction function (relates "amount" of drug at the effect site to E). The functions phi and ce delta are expressed as cubic splines for maximum versatility. Pharmacologic data collected after the administration of two different doses by i.v. infusion are analyzed simultaneously to estimate the function parameters. This experimental design addresses the fact that phi and ce delta cannot be uniquely estimated from the results of a single dose experiment. The unknown f from a test treatment is then estimated by applying an implicit deconvolution method to the pharmacologic data collected during that treatment. The method was tested with stimulated data. The method and the model were further evaluated by application to a clinical study of verapamil (V) pharmacodynamics in 6 healthy volunteers. Simulations showed that the method is accurate and precise in the presence of a high degree of measurement error, but large intrasubject variability in the model functions can result in biased estimates of the amount absorbed. The method produced reasonably accurate estimates of the V input rate and systemic availability (F) in the 6 human volunteers though there was a trend towards underestimation (estimated total F% = 93.6 +/- 14 vs. the true F% of 100).     

Threat-expectancy, word frequencies, and perceptual pre-recognition hypotheses.

"In order to investigate whether delayed perceptual report of threatening words would occur under conditions of threat-expectancy in an experimental setup which makes possible examination of the operation of possible conscious inhibition as well as differential word frequencies, 59 Ss were given a series of 16 booklets, each containing 30 carbon copies of one five-letter stimulus word, to decipher. Eight of these words were considered neutral and eight threatening… . Significantly more trials were required for correct report of threat words as compared to neutral ones. No correlation between number of trials required for correct identification of the test words and word frequency was found… . The findings are interpreted as consistent with a concept of perceptual defense." 20 references. (PsycINFO Database Record (c) 2010 APA, all rights reserved)