Abnormal Latency Research Articles

Numerical deficits in a single case of basal ganglia dysfunction

The present investigation assesses specific numerical difficulties in a patient (SJ) with basal ganglia (BG) dysfunction. While previous studies on number processing in BG disorders typically tested arithmetic facts by production tasks, the present study uses production, recognition (verification, multiple-choice) and indirect (number-matching) arithmetic tasks. Patient SJ was severely impaired in production and to a lesser extent in verification and multiple-choice tasks. In number-matching, an abnormal latency pattern was found. This study extends previous research by indicating that BG dysfunction may not only affect production processes and sequencing, as was found in previous investigations, but may lead to a breakdown of semantic relationships of arithmetic facts.

Simultaneous Measurement of Perceptual and Motor Cortical Potentials

Psychomotor slowing is a common manifestation of traumatic brain injury. Previous electrophysiological studies of traumatic brain injury have focused on abnormal attentional and perceptual responses to incoming stimuli. We hypothesize that traumatic brain injury is also associated with abnormal cortical components of motor execution. To test this hypothesis, we analyzed event-related potentials of 22 subjects (11 with a history of severe traumatic brain injury and 11 age-matched healthy subjects) during oddball discrimination tasks. In addition to the usual stimulus-locked averaging of electrophysiological data to reveal cognitive components, such as the P300, we also analyzed subjects' response-locked data to reveal motor potential waveforms. To focus on generalized effects across modality, analyses were performed on composite measures from both auditory and visual event-related potentials. (1) Traumatic brain injury subjects had abnormal P300 responses (with reduced amplitude and prolonged latency) in both sensory modalities. (2) Traumatic brain injury subjects' motor potential waveforms showed significantly reduced amplitude in both sensory modalities. (3) Abnormalities in P300 latency, amplitude, and motor potential amplitude (effect sizes = 1.2-1.5 SD) were greater than behavioral slowing, as measured by reaction times (0.7 SD). (4) P300 latency and motor potential amplitude together accounted for much of the reaction time prolongation (r = 0.73). This study demonstrates the value of concurrently analyzing stimulus-locked and response-locked event-related potential data to evaluate cortical components of perceptual and motor processing. The present findings indicate that patients with traumatic brain injury have impairments in both the perceptual interpretation of incoming stimuli and the execution of motor responses and that both abnormalities contribute to psychomotor slowing in patients with traumatic brain injury.

Abnormal short latency afferent inhibition in early Alzheimer’s disease: a transcranial magnetic demonstration

The pathogenesis of Alzheimer's disease (AD) appears to involve several different mechanisms, the most consistent of which is an impairment of cholinergic neurotransmission; however, there is controversy about its relevance at the early stage of disease. A transcranial magnetic stimulation (TMS) protocol based on coupling peripheral nerve stimulation with motor cortex TMS (short latency afferent inhibition, SAI) may give direct information about the function of some cholinergic pathways in the human motor cortex. We evaluated SAI in a group of patients with early diagnosis of AD and compared the data with that from a control group. The amount of SAI was significantly smaller in early AD patients than in controls. This study first provides physiological evidence that a central cholinergic dysfunction occurs in the earlier stages of AD. Identification of SAI abnormalities that occur early in the course of AD will allow earlier diagnosis and treatment with cholinergic drugs.

Significance of sympathetic skin response in diagnosis diabetic small fiber neuropathy

To investigate the significance of sympathetic skin response (SSR) in the diagnosis of diabetic small fiber neuropathy. 38 diabetic patients with paraesthesia and 30 healthy controls underwent SSR test on the 4 limbs. The latencies of the initiation and waves N and P of SSR were analyzed. The results of nerve conduction velocities of these patients with paraesthesia were normal. The latencies of the initiation and waves N or P in SSR were prolonged in 37 limbs of the 38 patients, and there was no SSR response in 21 limbs. The latencies of the initiation and waves N and P of SSR test in both upper extremity and lower extremities were prolonged significantly in the diabetic patients as compared to the controls (all P < 0.05). The frequency of abnormality in the latency of SSR was 51% in the lower extremities, and 38% in the upper extremities. The frequency of abnormal latency of SSR in the lower extremities was higher, however, not significantly, than that in the upper extremities (P > 0.05). Twenty-eight of the 38 patients (74%) demonstrated abnormal SSR in at least one limbs. SSR can be used to detect the early dysfunction of the small fibers in diabetic peripheral neuropathy, especially in the diabetic patients with normal nerve conduction velocities. SSR test may be a useful and sensitive neuroelectrophysiologic testing for the early diagnosis of diabetic small fiber neuropathy.

Prognostic Value of Somatosensory-Evoked Potentials in the Surgical Management of Cervical Spondylotic Myelopathy

Preoperative somatosensory-evoked potentials (SEPs) were retrospectively analyzed and classified, and compared with surgical outcome. To evaluate the value of the preoperative SEP waveform in predicting the clinical outcome after surgical management of cervical spondylotic myelopathy (CSM). SEPs have played an important role in spinal surgery. However, the value of SEPs in predicting the outcome of surgery for CSM remains controversial. This study enrolled 76 CSM patients who underwent surgical intervention. Median nerve SEPs were recorded before surgery. The Japanese Orthopedic Association (JOA) scoring system was used to evaluate the neurologic function before surgery and at postoperative follow-up at 1, 3, 6, 12, and 24 months. Patients were divided into 5 groups according to the classification of their preoperative SEP waveforms. Group I patients had normal SEPs, group IIa had normal latency and abnormal amplitude, group IIb had abnormal latency and normal amplitude, group III had abnormal latency and amplitude, and group IV had immeasurable waveforms. The myelopathic disability scores and surgical outcomes in different groups were compared by the Kruskal-Wallis test. The SEP classification was found to be significantly associated with the JOA score (Pearson's chi test, chi = 53.9, P < 0.05). There were no significant differences in JOA score recovery at different follow-up times within any SEP group. At 24 months after surgery, there was no significant difference in the recovery ratio between groups I and IIa, or between groups IIb and III (Kruskal-Wallis test, P > 0.05). However, the recovery ratio was significantly higher in groups I and IIa than in all the other groups (Kruskal-Wallis test, P < 0.05), and in groups IIb and III than in group IV (Kruskal-Wallis test, P < 0.05). SEP classification correlates well with CSM disability and postoperative recovery ratio. Median nerve SEP recordings would be a valuable and practical tool for the diagnosis and prognosis of myelopathy.

Canadian and American Sex Therapists' Perceptions of Normal and Abnormal Ejaculatory Latencies: How Long Should Intercourse Last?

Lay public perceptions about how long intercourse should last are discrepant from objective data on ejaculatory latencies. This may be problematic as the subjective interpretation of latency is a factor related to perceived distress with length of intercourse. Quantify the opinion of expert sex therapists as to what are "adequate,""desirable,""too short," and "too long" intravaginal ejaculatory latencies. Method. A random sample of members of the Society for Sex Therapy and Research in the United States and Canada was surveyed. Intravaginal ejaculatory latency, in minutes, for four different conditions: coitus that lasts an amount of time that is "adequate,""desirable,""too short," and "too long." Results. The interquartile range for the sex therapists' opinions regarding an "adequate" length for ejaculatory latency was from 3 to 7 minutes; "desirable" from 7 to 13 minutes; "too short" from 1 to 2 minutes; "too long" from 10 to 30 minutes. Therapists' beliefs about ejaculatory latencies were consistent with objective data on ejaculatory latency and were not affected by therapist demographic characteristics such as sex or experience. These results suggest that the average sex therapist believes that intercourse that lasts 3 to 13 minutes is normative and not prima facie worthy of clinical concern. Dissemination to the public of these results may change lay expectations for intravaginal ejaculatory latency and prevent distress. These results may also be beneficial to couples in treatment for sexual problems by normalizing expectations.

Validación de la Escala de Somnolencia de Epworth

Validating the Epworth sleepiness scale (ESS-VC) for use in Colombia . Individuals were included who consulted sleep centres in Bogotá, Pereira and Cali ( Colombia ). Study design consisted of eight phases: a pilot study for assessing the Spanish version of the scale, translation and retro-translation of the original ESS, a pilot test for evaluating understanding (n=20), validating appearance (experts, n=18), internal consistency (n=120), validating concurrent and discriminating criteria (n=150) with parallel polysomnography, reproducibility (n=15) and sensitivity to change (n=100). ESE-VC presented suitable internal consistency (Cronbach's Alpha=0,85). It identified patients suffering from severe sleepiness, according to pathology (K Wallis Chi2=19,81, p=0.003). It was clinically significant in discriminating patients according to sleep apnoea severity and abnormal sleep latency (Chi2=5,391, p=0.1453) in ways, and also in REM sleep latency (Chi2=9,015, p=0.0291). It is reproducible and sensitive to change. ESS-VC compared well with the original version. It is well adapted to urban life conditions in the Colombian adult population, reliable, valid and sensitive to reported changes. It had clinically and statistically significant correlation with polysomnography.

Ulnar Neuropathy at or Distal to the Wrist: Traumatic Versus Cumulative Stress Cases

Chiodo A, Chadd E. Ulnar neuropathy at or distal to the wrist: traumatic versus cumulative stress cases. Objective To identify clinical and electromyographic characteristics of ulnar neuropathy at or below the wrist, comparing those caused by unitary trauma with those caused by suspected cumulative stress. Design Retrospective case series. Setting University hospital electromyography laboratory. Participants Patients with electrodiagnostic evidence of an ulnar neuropathy at or distal to the wrist over a 3-year period. Forty-seven hands from 42 patients (age range, 20−80y; mean, 52y) were identified and evaluated in this study. Interventions Record review of clinical history, physical examination, electromyography, and treatment. Main Outcome Measures Etiology of injury, physical signs and symptoms, and electromyographic testing results. Results Ulnar neuropathy at or distal to the wrist is commonly mischaracterized because of other mononeuropathies in the upper extremity and because of peripheral polyneuropathy. Ulnar neuropathy because of cumulative stress presents typically with sensory symptoms (63%) and a normal examination (71%), whereas trauma cases present with motor with or without sensory symptoms (92%) with motor abnormalities (92%) confirmed on examination. Traumatic cases are characterized by electromyography by decreased sensory and motor-evoked amplitudes, prolonged motor distal latencies, and abnormal needle examination. The amplitude changes are noted comparing with laboratory norms and comparing side to side. No characteristic pattern of abnormalities on electromyography is noted in the cumulative stress cases. Patients with no motor symptoms, regardless of etiology, are more apt to have sensory distal latency prolongation, whereas those with motor symptoms have motor amplitude and needle examination abnormalities. Conclusions Traumatic ulnar neuropathy at or distal to the wrist is characterized by motor symptoms and sensory and motor axonal loss by electromyography, whereas cumulative stress cases have sensory symptoms and electromyographic findings that are highly variable and noncharacteristic. Patients with no motor symptoms are more apt to show sensory distal latency abnormalities on electromyography, whereas those with motor symptoms show motor-evoked amplitude and needle electromyography abnormalities.

Balance control in Sensory Neuron Disease

Objective Balance control under static and dynamic conditions was assessed in patients with Sensory Neuron Disease (SND) in order to shed further light on the pathophysiology of ataxia. Methods Fourteen patients with diabetic polyneuropathy and 11 with SND underwent clinical and neurophysiological evaluation, stabilometric recording of body sway during quiet stance with and without vision, stereometric analysis of body segment displacement while riding a platform translating in anterior–posterior direction with and without vision (dynamic condition), and EMG recording of leg muscle responses to abrupt stance perturbation produced by rotation of a supporting platform. The findings were compared to those of age matched normal subjects. Results Clinical and neurophysiological evaluation revealed a more severe motor impairment in patients with diabetes than SND, while sensory impairment was superimposable. Some patients with SND had vestibular dysfunction of diverse severity. Body sway during stance was larger in patients with SND than diabetes with and without vision. In the stance perturbation condition, the latency of the long-loop EMG response to platform rotation was disproportionately increased with respect to the spinal response in the SND but not in diabetic patients. Under dynamic condition, patients with SND oscillated more than diabetic patients and several of them easily lost balance with eyes closed. Conclusions Patients with SND show severe unsteadiness under both static and dynamic conditions, particularly with eyes closed. The patchy sensory loss of SND, disrupting sensation from territories other than the lower limbs and possibly including the vestibular nerve, could be responsible for this instability. Ataxia is correlated to the abnormal latency of the muscle responses to stance perturbation. Since increased response latencies cannot be attributed to a vestibular deficit, the deterioration of equilibrium control would be ascribed mainly to the degeneration of the central branch of the afferent fibres. Significance Measures of body balance under quiet stance and dynamic conditions can provide relevant diagnostic information as to the pathophysiology and severity of ataxia and viability of the central branch of the sensory fibres, and help in separating patients with peripheral neuropathy from patients with loss of sensory neurones.

Impaired Objective Daytime Vigilance in Obesity-Hypoventilation Syndrome: Impact of Noninvasive Ventilation

Background:Obesity-hypoventilation syndrome (OHS) is efficiently treated by noninvasive ventilation (NIV). Sleep respiratory disturbances, reduced ventilatory drive, and excessive daytime sleepiness (EDS) are commonly reported, but their relationships remain unclear.Objectives:To characterize sleep breathing disorders encountered in patients with OHS, to compare low and normal CO2responders in terms of sleep abnormalities, subjective and objective measures of EDS, and to measure the changes induced by NIV on these parameters.Methods:At baseline and after 5 nights of NIV, 15 consecutive patients (mean [± SD] age, 55 ± 9 years; mean body mass index, 38.7 ± 6.1 kg/m2; Paco2, 47.3 ± 2.3 mm Hg) prospectively underwent polysomnography, CO2ventilatory response testing, Epworth sleepiness scale scoring, and the Oxford Sleep Resistance (OSLER) test, which is an objective vigilance test.Results:OHS patients exhibited obstructive sleep apnea syndrome (mean apnea-hypopnea index, 62 ± 32 events per hour) and rapid eye movement (REM) sleep hypoventilation (mean REM sleep time, 35 ± 33%). Baseline CO2sensitivity was significantly related to the proportion of hypoventilation during REM sleep (r= 0.54; p = 0.037). Six patients showed abnormal sleep latencies during the OSLER test (71% of the low CO2responders vs 14% of the normal CO2responders). Low CO2responders exhibited significantly shorter sleep latencies during the OSLER test (23 ± 14 vs 37 ± 8 min, respectively; p = 0.05). Using NIV, diurnal blood gas levels were improved and REM sleep hypoventilation were suppressed. Objective sleepiness was improved in low CO2responders (p = 0.04).Conclusion:In OHS patients, the lower the daytime CO2response, the higher the proportion of REM sleep hypoventilation and daytime sleepiness. Short-term therapy with NIV improves all of these parameters.

Sensitivities of Sensory Nerve Conduction Study Parameters in Carpal Tunnel Syndrome

It is generally accepted that median sensory nerve conduction studies are more sensitive than motor nerve conduction studies in the electrodiagnostic evidence of carpal tunnel syndrome (CTS). This study was conducted to compare the sensitivities of various parameters of sensory nerve conduction studies in the diagnosis of CTS. This prospective study included 88 consecutive patients (151 hands) with CTS and 106 control subjects. CTS was diagnosed clinically by two neurologists. Median sensory nerve responses with wrist stimulation were determined. The onset and peak latencies, peak-to-peak amplitudes, negative peak duration, and area were measured. The differences between the peak and onset latencies were also calculated as a measure of waveform temporal dispersion. Among each measured parameter, values between the 2.5th and the 97.5th percentile range of the control subjects served as the normal limits. Among the 151 hands with suspected CTS, five (3.3%) had normal electrodiagnostic studies and 146 (96.7%) had at least one abnormal electrodiagnostic study. Among the 146 hands with an abnormality, 138 had abnormal onset latency, 143 had abnormal peak latency, and 88 had abnormal difference between peak and onset latency. In addition, 87 had abnormal amplitude, 70 had abnormal duration, and 59 had abnormal area. The sensitivity was 91.4% for onset latency, 94.7% for peak latency, 58.3% for difference between peak and onset latency, 57.6% for amplitude, 46.4% for duration, and 39.1% for area. Our study shows that in patients with CTS, the most sensitive sensory nerve conduction parameter is the peak latency. Studying various additional sensory nerve conduction parameters did not significantly increase the diagnostic yield.

Visual-Evoked Potentials to Onset of Chromatic Red-Green and Blue-Yellow Gratings in Parkinson’s Disease Never Treated With L-Dopa

The differential dysfunction of chromatic and achromatic visual pathways in early Parkinson's disease (PD) was evaluated by means of visual-evoked potentials (VEPs) recorded in 12 patients (mean age 60.1 +/- 8.3 years; range 46 to 74 years) in the early stages of PD and not yet undergoing treatment with L-dopa, and in 12 age-matched controls. Visual stimuli were full-field (14 deg) equiluminant red-green (R-G), blue-yellow (B-Y), and black-white (B-W) sinusoidal gratings of two cycles per degree, presented in onset (300 milliseconds)--offset (700 milliseconds) mode, at two contrast (K) levels (90% and 25%). The VEP mean latencies were significantly more delayed in PD patients than in controls for chromatic than for luminance stimuli, in particular for B-Y stimuli of low contrast (K90%: B-W = 6.6 milliseconds, R-G = 3.34 milliseconds, B-Y = 15.48 milliseconds; K25%: B-W = 7.8 milliseconds, R-G = 14.8 milliseconds, B-Y = 28.9). Latencies of chromatic VEPs were more variable that achromatic VEP latencies in both normal subjects and PD patients. Therefore, the frequency of latency abnormalities (within 30%) was not significantly different for the three visual stimuli. Our results show that, in addition to achromatic VEPs, chromatic VEPs are impaired in early PD patients not yet undergoing L-dopa therapy, indicating an acquired color deficiency in these patients. The greater delay for the B-Y VEPs suggests a higher vulnerability of visual blue-cone pathway in the early stages of the disease. However, the overall sensitivity of chromatic VEPs in detecting early visual impairment in PD is comparable with that of achromatic VEPs.

Effects of Prolonged Wrist Flexion on Transmission of Sensory Information in Carpal Tunnel Syndrome

Carpal tunnel syndrome presents a constellation of symptoms which include discomfort (eg, pain, paraesthesia) and diminished sense of touch. This exploratory study simultaneously measured changes in tactile threshold and discomfort ratings during prolonged wrist flexion in symptomatic patients from a rehabilitation clinic and from a control population. Prolonged (15 min) wrist flexion significantly increased tactile threshold and discomfort ratings above baseline levels in both symptomatic and control populations. Sixty-two percent of the symptomatic sample was found to have abnormal conduction latency. Tactile threshold in symptomatic subjects with normal conduction latency (n = 13) did not differ significantly from control subjects (n = 36) at baseline but showed significant elevation during wrist flexion. In contrast, subjects with abnormal conduction latency (n = 21) exhibited significant elevation relative to control subjects at baseline and throughout wrist flexion as well as a slower recovery after flexion. Conduction latency correlated with baseline (r = .52, P < .0001) and 15-min (r = .67, P < .0001) tactile threshold for the entire subject population, as well as 15-min threshold (r = .53, P = .013) for the subpopulation with abnormal conduction latency. At 2.5 min after flexion, correlation was significant for whole (r = .64, P < .0001) and abnormal conduction latency (r = .58, P = .0063) samples. Regression slope of tactile threshold versus conduction latency was significantly greater than zero and did not differ significantly from linearity. The study demonstrates that increases in mechanosensory threshold and discomfort ratings during prolonged wrist flexion are more profound (and recovery less rapid) in patients with electrophysiologic evidence of injury. Perspective This study demonstrates a provocative procedure that enhances the symptoms of carpal tunnel syndrome. This measure may help clinicians discriminate median nerve compression from other types of peripheral nerve injury and help researchers investigate the impact of mechanical stress, tissue compression, and vascular stasis on compression-related neuropathy.

Diagnostic value of vestibular evoked myogenic potentials in cerebellar and lower-brainstem strokes

Background Vestibular evoked myogenic potentials (VEMPs) provide assessment of vestibular function. They consist in picking up compound muscle action potentials in the sternocleidomastoid (SCM) muscles in response to auditory stimulation of the vestibulum. VEMP testing has found application mainly in peripheral vestibular disorders, whereas reports about VEMPs in central vestibular lesions are rather scarce. Aims of the study Based on the physiological connections between the cerebellum and the vestibular nuclei, we investigated the influence on VEMPs of cerebellar and lower-brainstem strokes. We examined whether or not this method may be suitable as a clinical tool for the evaluation of the extent of cerebellar strokes. Patients and methods Nineteen patients with cerebellar ischemic stroke and 15 patients with lower-brainstem ischemic stroke (11 in the pons, four in the medulla) were included. The latencies and amplitudes of P13 and N23 in both groups of patients were compared with those obtained in a control group of 53 normal individuals. Results VEMP responses were obtained in all patients and controls. At the group level, mean peak latencies and amplitudes, and the number of subjects with significantly deviant values did not differ between patients and controls. There were no latency or amplitude differences ipsilaterally or contralaterally to the lesion. At the individual level, there was no correlation between laterality of lesion and that of P13 or N23 abnormalities in patients with cerebellar strokes; however, there were two patients (one pontine, one medullar stroke) who presented P13 and N23 latency abnormalities ipsilaterally to the lesion. Conclusion Cerebellar strokes do not influence VEMPs. Moreover, despite previous reports, we were unable to find at a group level any statistically significant VEMP changes in patients with lower-brainstem strokes as compared with controls. Therefore, VEMPs do not appear a suitable tool for assessment of brainstem integrity in patients with posterior fossa strokes. However, they could constitute a sensitive method for documentation of involvement of the central vestibular pathways in patients with brainstem stroke.

Increased REM Sleep Associated with Melatonin Deficiency after Pinealectomy: A Case Study

The objectives of the investigation were to assess hypersomnia, which progressively appeared in a young patient after a pinealectomy, chemotherapy, and radiotherapy for a typical germinoma, as well as the potential benefit of melatonin administration in the absence of its endogenous secretion. 24 h ambulatory polysomnography and the Multiple Sleep Latency Test (MSLT) were performed; in addition, daily plasma melatonin, cortisol, growth hormone, prolactin, and rectal temperature profiles were determined before and during melatonin treatment (one 2 mg capsule given nightly at 21:00 h for 4 weeks). MSLT showed abnormal sleep latency and two REM sleep onsets. Nighttime total sleep duration was lengthened, mainly as a consequence of an increased REM sleep duration. These parameters were slightly modified by melatonin replacement. Plasma melatonin levels, which were constantly nil in the basal condition, were increased to supraphysiological values with melatonin treatment. The plasma cortisol profile showed nycthemeral variation within the normal range, and the growth hormone profile showed supplementary diurnal peaks. Melatonin treatment did not modify the secretion of either hormone. The plasma prolactin profile did not display a physiological nocturnal increase in the basal condition; however, it did during melatonin treatment, with the rise coinciding with the nocturnal peak of melatonin concentration. A 24 h temperature rhythm of normal amplitude was persistent, though the mean level was decreased and the rhythm was dampened during melatonin treatment. The role of radiotherapy on the studied parameters cannot be excluded; the findings of this case study suggest that the observed hypersomnia is not the result of melatonin deficiency alone. Overall, melatonin treatment was well tolerated, but the benefit on the sleep abnormality, especially on daytime REM sleep, was minor, requiring the re‐introduction of modafinil treatment.

Upper Extremity Mononeuropathy Among Engineers

The objectives of this study were to estimate the prevalence of mononeuropathy at the wrist among engineers who use computers and to identify associated risk factors. This is a cross-sectional study of 202 engineers using questionnaires and electrophysiological nerve testing. The definition for median or ulnar mononeuropathy required the combination of distal upper extremity discomfort and abnormal distal motor latency. The prevalence of neuropathy at the wrist among engineers was 10.3% (right median), 3.4% (left median), 1.8% (right ulnar), and 2.9% (left ulnar). Logistic regression analysis identified three variables with positive associations (body mass index, hours of computer use, and antihypertensive medication) and three variables with negative associations (typing speed, driving hours, total break time). Mononeuropathies at the wrist occur among computer-using engineers and are related to a number of factors, including hours of computer use.

Attention and memory dysfunctions in mild multiple sclerosis

This study investigated the relationship between clinical symptoms and cognitive dysfunction in multiple sclerosis. Cognitive dysfunction and visual evoked potentials (VEPs) were studied in patients free of physical disability and mildly to moderately disabled patients with multiple sclerosis (MS). Disability-free patients (EDSS < or = 1.5; n = 13), mildly to moderately disabled patients (EDSS ranging from 2 to 6; n = 13) and a healthy matched control group (n = 16) were examined with respect to attention, verbal and nonverbal memory and early visual processing (VEPs). Disability-free patients showed mild impairments on phasic alertness and divided attention. Deficits were more pronounced in mildly to moderately disabled patients who were additionally impaired with respect to non-verbal memory. Despite adequate visual acuity, one half of all patients showed abnormal VEP latencies for both eyes at the same time. The findings suggest that cognitive deficits are already present in multiple sclerosis even in the absence of physical disability. Even with normal visual acuity, perceptual impairments should be considered as part of the CNS affection.

Using automated morphometry to detect associations between ERP latency and structural brain MRI in normal adults

Despite the clinical significance of event-related potential (ERP) latency abnormalities, little attention has focused on the anatomic substrate of latency variability. Volume conduction models do not identify the anatomy responsible for delayed neural transmission between neural sources. To explore the anatomic substrate of ERP latency variability in normal adults using automated measures derived from magnetic resonance imaging (MRI), ERPs were recorded in the visual three-stimulus oddball task in 59 healthy participants. Latencies of the P3a and P3b components were measured at the vertex. Measures of local anatomic size in the brain were estimated from structural MRI, using tissue segmentation and deformation morphometry. A general linear model was fitted relating latency to measures of local anatomic size, covarying for intracranial vault volume. Longer P3b latencies were related to contractions in thalamus extending superiorly into the corpus callosum, white matter (WM) anterior to the central sulcus on the left and right, left temporal WM, the right anterior limb of the internal capsule extending into the lenticular nucleus, and larger cerebrospinal fluid volumes. There was no evidence for a relationship between gray matter (GM) volumes and P3b latency. Longer P3a latencies were related to contractions in left temporal WM, and left parietal GM and WM near the interhemispheric fissure. P3b latency variability is related chiefly to WM, thalamus, and lenticular nucleus, whereas P3a latency variability is not related as strongly to anatomy. These results imply that the WM connectivity between generators influences P3b latency more than the generators themselves do.

Determining abnormal interocular latencies of multifocal visual evoked potentials

To describe methods for measuring interocular latency differences of multifocal visual evoked potentials (mfVEP) and for determining regions with abnormal interocular latencies in patients. The mfVEPs from 100 individuals with normal visual fields and normal fundus examinations were analyzed. Individuals ranged in age from 21.6 to 92.4 years. The stimulus was a 60 sector, pattern-reversing dartboard display. Each sector had 16 checks, 8 white (200 cd/m2) and 8 black (< 1 cd/m2). Interocular latency was measured as the temporal shift producing the best cross-correlation value between the corresponding responses of each eye. The 'corrected interocular latency' was defined as the difference between this shift and the mean interocular latency (shift) for a particular sector and recording channel. The variability of the corrected interocular latency decreased as the signal-to-noise ratio (SNR) of the mfVEP responses increased. For example, the 95% confidence intervals decreased from over 16 ms to under 4 ms as SNR increased. Grouping and summing the responses also lead to an increase in SNR and a decrease in the confidence interval. The results of various cluster criteria were also derived. A cluster criterion (e.g. two or more contiguous points within a hemisphere exceeding a given confidence interval), can serve to increase the specificity for detection of eyes or individuals with abnormal interocular latencies. For example, while 21% of the eyes had 3 or more points exceeding the 5% confidence interval, only 1.8% of the eyes had a cluster of 3 or more of these points. Finally, interocular latency was only weakly correlated with age (r = 0.26). In testing for abnormalities in interocular latencies, the confidence interval should be based upon the SNR of the response. Grouping and summing responses to increase SNR or employing a cluster test may also prove useful.

Morphological and latency abnormalities of the mid-latency auditory evoked responses in schizophrenia: a preliminary report

Introduction: Evoked potential (EP) amplitude and latency abnormalities have been extensively examined in schizophrenia. Morphological abnormalities of the mid-latency auditory evoked responses (MLAERs; P50, N100, P200), on the other hand, received very little attention. Methods: Based on a priori defined set of morphological criteria, the morphology and latency of the MLAERs were blindly compared between stable outpatients with schizophrenia ( N=27) and age- and gender-matched healthy control subjects ( N=22). The morphology of the MLAERs was considered abnormal if one or more of the components fell outside the expected latency range, if one or more of the components were missing, or if a later occurring component was smaller in amplitude than an earlier occurring one. Results: Of the 27 schizophrenia subjects, 20 had waveforms that were deemed atypical, while only 8 from the control group were classified as atypical ( χ 2=5.52, p<0.02). The latencies of the P50 and N100 components, identified based on morphology, were significantly prolonged in schizophrenia patients. Conclusions: These preliminary data suggest that morphological abnormalities of the MLAERs in schizophrenia patients are significant and should be taken into consideration when examining the MLAERs of this patient population.