James T. Marsh

Far-field recorded frequency-following responses: Evidence for the locus of brainstem sources

Two experiments were performed to determine the brainstem origins of the scalp recorded auditory frequency-following response (FFR). The first was a study of FFR onset latency in which responses observed by direct recording from depth electrodes in brainstem auditory nuclei were compared with those obtained from the scalp. The mean onset latency of scalp recorded FFR (5.8 msec) closely approximated the 5.4 msec mean latency of response recorded from within the inferior colliculus (IC). In a second experiment, cooling of the IC greatly reduced or eliminated FFR both within this nucleus and at the scalp. FFR at the medial superior olive was unaffected during cooling. It was concluded that at moderate intensities of stimulation the primary source of scalp recorded FFR is the IC.

Frequency-following (microphonic-like) neural responses evoked by sound☆

Abstract 1. 1. An acoustically evoked response is described which reproduces the frequency and wave form of the stimulus. This frequency-following response (FFR) is recordable from gross electrodes in the central auditory pathway. 2. 2. The FFR differs from an acoustic stimulus of graded onset, and the cochlear microphonic response (CM), in that it has a sharp onset, a latency appropriate to the locus from which it is recorded, an amplitude burst at the onset and a decrement of amplitude over time. 3. 3. The frequency range of FFR increases with stimulus intensity. At 80 dB sound pressure level the range is approximately 500–5000 c/sec. For recordings from the cochlear nucleus these frequency limits are not influenced by Nembutal anesthesia. 4. 4. The wave form and amplitude of FFR vary with stimulus frequency and with laterality of stimulus input. 5. 5. In contrast to the auditory evoked potential, which can be recorded widely in the brain, FFR is recordable only within, or close to, the auditory pathway. We have observed it only at, and below the level of the inferior colliculus. 6. 6. FFR has implications for the neurophysiology of hearing which are different from those of the auditory evoked potential. Some of these are discussed.

Judgements of emotion in words and faces: ERP correlates

Visual event-related potentials (ERPs) to two types of stimuli (faces and words) were analyzed to determine the effects of the perceived emotional connotations of the stimuli (positive, neutral, or negative) in 10 right-handed normal functioning adult males. Principal component analysis (PCA) of the ERPs reveals 5 factors accounting for over 90% of the ERP waveform variance for both faces and words. In the facial data, two ERP components varied in amplitude according to the perceived emotional connotation of the stimulus. For the P3 component, neutrally rated stimuli produced significantly larger amplitudes than stimuli rated as positive or negative. This effect was lateralized to the left hemisphere. A later positive component, the slow wave (448-616 ms), manifested complementary effects, i.e. faces perceived as positive and negative produced larger amplitudes than those perceived as neutral over the right hemisphere. The verbal stimuli did not result in significant main effects for perceived emotional connotation, but produced subtle connotation-related differences in slow wave topography. Hemispheric asymmetries, unrelated to affective connotation, were evident in the verbal data, manifesting different patterns of lateralization depending on the ERP component. The results suggest that differential processing of emotional connotation affects ERP waveforms and that the effects can be understood in terms of ERP components known to be associated with more general aspects of cognitive processing.

Increased Susceptibility to Herpes Simplex in Mice Subjected to Avoidance-Learning Stress or Restraint.

Summary Stress induced in mice by avoidance-learning or by restraint resulted in an increased susceptibility to infection with the virus of herpes simplex.

Recombinant Human Erythropoietin Treatment May Improve Quality of Life and Cognitive Function in Chronic Hemodialysis Patients

Medical, psychological, and social adaptation (quality of life) as well as cognitive function were studied in 15 chronic stable hemodialysis patients before the onset of treatment with recombinant human erythropoietin (r-HuEPO), 1 month after stabilization of normal hematocrit levels, and 10 to 15 months after treatment onset. After r-HuEPO treatment, subjects had significantly higher hematocrits, markedly improved energy levels, and marginally improved global health. r-HuEPO treatment was also associated with progressively decreased levels of subject mood disturbance and dialysis-related stresses. Subjects had no increased participation in paid employment and only minimally increased participation in social and leisure activities at posttreatment data points. There was no significant improvement in cognitive function after treatment. r-HuEPO treatment appears to be associated with higher energy levels, significant psychological benefits, and minimal improvements in social adaptation. The effects on cognitive function merit further study.

Continuous-processing-related event-related potentials in children with attention deficit hyperactivity disorder

Visual information processing in children with attention deficit hyperactivity disorder (ADHD) was studied using event-related potentials recorded during two versions of the Continuous Performance Task (CPT). ADHD children made more errors, and had longer reaction times than normal children on both the single- and dual-target CPT. Event-related potential waveforms were normal in the ADHD children with reference to early processing stages, i.e., contingent negative variation, P1-N1 laterality, and processing negativities, suggesting that ADHD children did not differ in their level of preparedness or their ability to mobilize resources for target identification and categorization. With respect to later processing, P3 amplitude was reduced in the ADHD group, whereas P3 latency was longer than normal. ADHD children had a diminished late frontal negative component, suggestive of reduced involvement in postdecisional processing.

Contextual meaning effects on speech-evoked potentials

Responses to spoken words were recorded from scalp electrodes approximately over Wernickes and Brocas areas and over homotopic points on the nondominant hemisphere of adult right-handed humans. The waveform of averaged potentials evoked by the same word differed according to its contextual meaning. Thus, responses to the word “fire” differed when in the phrases “sit by the fire” and “ready, aim, fire.” Waveform differences were significantly greater for left hemisphere, than for right hemisphere loci. When context was made ambiguous, as in the phrases “fire is hot” and “fire the gun,” waveform differences disappeared.

Relationship of Dialysis Modality and Other Factors to Cognitive Function in Chronic Dialysis Patients

To determine if dialysis modality may be an independent factor in the level of cognitive function in chronic dialysis patients, cognitive function was studied in 17 pairs of continuous ambulatory peritoneal dialysis (CAPD) and center hemodialysis (CHD) subjects matched for sex, age, diabetic status, and interval since dialysis onset. Data on current metabolic, medical, psychological, and vocational function status were obtained. Neuropsychological (NP) measures included the Number Cancellation Protocol (NCP), Trailmaking test forms A and B (TMT A, TMT B), Symbol Digit Modalities (SDM), and the Rey Auditory Verbal Learning Test (RAVLT). The CAPD subject group had consistently more efficient cognitive function than the CHD subject group. Regardless of modality, the groups of subjects under age 51 and those who were vocationally active had significantly better NP performance. No cognitive function differences were found in groups categorized by sex or duration of dialysis. Creatinine levels were more highly correlated with NP scores than were BUN levels, with higher creatinine levels associated with better cognitive function. Serum calcium, CO2, total protein, albumin, and SGOT levels also were correlated with NP scores. CAPD may be more effective than HD in reversing uremic encephalopathy by mechanisms mostly unrelated to serum creatinine and BUN levels. Longitudinal studies will be needed to determine if dialysis modality is an independent factor in the degree of reversal of uremic encephalopathy.

Auditory potentials during acoustic habituation: Cochlear nucleus, cerebellum and auditory cortex

Abstract 1. 1. Amplitude changes of auditory EPs and of cortical background activity were studied during acoustic habituation in 5 cats with chronically implanted electrodes. Click stimuli were delivered to the unrestrained animals through earphones in order to hold acoustic input constant. 2. 2. Data were collected in both non-alerted (sleeping) and alerted conditions after 2, 4 and 6 h of click repetition. 3. 3. At the cochlear nucleus, no consistent amplitude change in EPs was observed. There was no amplitude difference between the non-alerted and alerted conditions. 4. 4. At the auditory cortex, a consistent and progressive loss of amplitude of EPs over time occurred for the alerted but not for the non-alerted condition. 5. 5. At the auditory cortex, the amplitude of EPs was larger in sleep than in the alerted condition. 6. 6. At the auditory cortex, the amplitude of EPs covaried with the amplitude of background activity across the non-alerted and alerted conditions, and also within each condition. It is suggested that amplitude of cortical EPs is a function of the state of cortical synchrony, regardless of how this state of synchrony is produced. 7. 7. Large auditory EPs were recorded from the flocculus and adjacent cerebellum. Despite great variability, these showed a significant loss of amplitude during acoustic habituation for the alerted, but not for the non-alerted condition. In addition, they were larger in the sleep than in the alerted condition.

Event-related potential correlates of linguistic information processing in schizophrenics.

Event-related potentials (ERPs) were recorded from adult schizophrenics and age- and education-matched normal controls during performance of an idiom recognition task involving judgments of the meaningfulness of idiomatic, literal, and nonsense phrases. Schizophrenics produced more errors and had prolonged reaction times while attempting to correctly differentiate meaningful from meaningless phrases. An ERP correlate of that deficit was a larger than normal N400 to idioms and literals, with no difference in N400 amplitude to nonsense phrases. This result was interpreted as evidence that the influence of the linguistic context provided by the first word of two-word idiomatic and literal phrases is reduced in schizophrenia. Schizophrenics also showed reduced amplitude P300.