Authors:
Robert T. Wertz
Nina F. Dronkers
J. K. Shapiro
Robert T. Knight
Date: 1991
Electrophysiological measures of recognition memory
Evoked potential studies of attention capacity in human frontal lobe lesions
Authors:
Robert T. Knight
Date: 1991
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Abstract:
focus on EP [evoked potentials] and ERP [event-related potentials] studies of patients with frontal lobe damage frontal lobe syndromes / gating deficits / focused sustained attention deficits / phasic attention deficits (PsycINFO Database Record (c) 2012 APA, all rights reserved)
P300 generation by novel somatosensory stimuli
Authors:
Shuhei Yamaguchi
Robert T. Knight
Date: 1991
DOI: 10.1016/0013-4694(91)90018-Y
PubMed: 1701715
Abstract:
Event-related potentials (ERPs) to task-relevant target and task-irrelevant novel stimuli were recorded in a somatosensory discrimination task. Subjects pressed a button to mechanical taps of the fifth finger (targets, P = 0.12), randomly interposed in sequences of taps to the second finger (standards, P = 0.76). Two types of infrequent novel stimuli were delivered; one was a mechanical tap to the third or fourth finger (tactile novels, P = 0.06), another was an electric shock at the wrist (shock novels, P = 0.06). Correctly detected targets generated a parietal maximal P300 (P3b, latency 335 msec). Shock novels generated a central maximal P300 with a shorter peak latency (298 msec) than the P3b. Tactile novels generated a P300 with a scalp distribution comparable to the shock novels. Unlike the P3b, P300 amplitude to both the shock and tactile novel stimuli habituated by 20-30% across the first several stimulus presentations. These results indicate that, similar to the auditory and visual modality, task-irrelevant novel somatosensory stimuli generate a novelty P300 ERP. Differences in scalp distribution, latency and habituation characteristics suggest that the novelty P300 may have contributions from intracranial generators independent from target P300 sources.
Age effects on the P300 to novel somatosensory stimuli
Authors:
Shuhei Yamaguchi
Robert T. Knight
Date: 1991
DOI: 10.1016/0013-4694(91)90184-6
PubMed: 1706251
Abstract:
Event-related brain potentials (ERPs) to somatosensory task-relevant targets and task-irrelevant novel (tactile and shock) stimuli were studied in 30 subjects between the ages of 18 and 79. Target and novel P300 latencies increased linearly with age at comparable rates. P300 amplitudes and scalp topographies also changed with age. P300 amplitudes remained constant at frontal sites and decreased at central and parietal sites for both target and novel stimuli with increasing age. The current results extend the age-related novel P300 changes reported in the auditory and visual modalities to the somatosensory system. The age-related amplitude reduction at posterior scalp sites supports independent contributions of frontal and posterior association cortex to P300 generation.
Lack of age effects on human brain potentials preceding voluntary movements
Authors:
Jaswinder Singh
Robert T. Knight
David L. Woods
Dennis J. Beckley
Clay Clayworth
Date: 1990
PubMed: 2097580
Abstract:
We examined age effects on Movement related potentials (MRPs) in 13 young (mean age = 29.3 years) and 13 old (mean age = 67.2 years) normal adults in right, left and bimanual self-paced button press conditions. Both the groups generated a slowly rising readiness potential (RP) at about 1000 ms, a negative shift (NS') at about 450 ms and a motor potential (MP) at about 100 ms prior to movement. The RP was symmetrical, bilaterally distributed and maximal at the vertex in all conditions in both the groups. Both the groups produced contralateraUy enhanced NS' and MP compo- nents in unimanual conditions. In contrast to prior reports, topographical distribution, onset latency and mean amplitude were comparable between young and old subjects for the RP, NS' and MP components of the MRP. The results indicate that motor programming as indexed by MRPs is unaffected by normal aging.
Evoked potential mapping of auditory and somatosensory cortices in the miniature swine
Abstract:
The miniature swine (Sus scrofa) is a desirable model for certain electrophysiological studies because of its large brain, ready availability and low cost. We report our findings regarding the location of the auditory and somatosensory cortices obtained by cortical surface evoked potential mapping. Data were collected from 11 animals under general endotracheal anesthesia. Consistent positive potentials were obtained for both auditory (P24) and median nerve somatosensory (P26) stimulation. The auditory region was centered around the lateral (sylvian) fissure; the somatosensory region was centered around the central (dorsomedial suprasylvian) fissure. In the miniature swine the locations of the auditory and somatosensory cortices are comparable to those found in other species.
Gating of somatosensory input by human prefrontal cortex
Abstract:
Somatosensory evoked potentials (SEPs) to median nerve stimulation were recorded in controls and in patients with focal lesions in dorsolateral prefrontal cortex (PFCx). Unilateral PFCx lesions increased the amplitude of the P26 component generated in postcentral areas 1 and 2. The amplitudes of the N28, P45 and N67 SEP components recorded over post-rolandic and frontal electrodes were also enhanced by PFCx damage. In contrast, the N19 component generated in postcentral area 3b was unaffected by PFCx lesions. The results indicate that PFCx exerts inhibitory modulation on sensory processing that may be mediated by corticocortical PFCx-parietal connections.
Neurogenic communication disorders in remote settings
Authors:
Robert T. Wertz
Nina F. Dronkers
Gregory K Shenaut
Robert T. Knight
Date: 1990
Movement related potentials in patients with MPTP-induced Parkinsonism and early and late Parkinsonism
Authors:
Jaswinder Singh
B. R. Bloem
Robert T. Knight
William Jagust
David L. Woods
Dennis J. Beckley
J. Tetrud
J. W. Langston
Date: 1990
Effects of unilateral temporal-parietal lesions on interference between global and local levels in a divided attention task
Authors:
M. Lamb
Lynn C. Robertson
Robert T. Knight
Date: 1990
ERPs in patients with focal brain lesions
Posterior/Anterior contributions in responding to global and local levels of visual stimuli
Authors:
Lynn C. Robertson
M. Lamb
Robert T. Knight
Date: 1990
Neural mechanisms of event related potentials: evidence from human lesion studies
Authors:
Robert T. Knight
Date: 1990
Abstract:
Study of humans with neurochemical deficits, implanted intracranial electrodes, and focal brain lesions has contributed data on the neural systems involved in generation of certain scalp-recorded, event-related potentials (ERPs) / evidence from each of these endeavors will be reviewed in turn neurochemical syndromes / intracranial recording / focal brain lesions.
Component Mechanisms Underlying the Processing of Hierarchically Organized Patterns: Inferences From Patients With Unilateral Cortical Lesions
Abstract:
Subjects identified target letters that occurred randomly at the local or global level in a divided attention task. The visual angle of the stimuli was varied. Neurologically intact controls showed a reaction time advantage for local targets which increased as visual angle increased. Patients with lesions centered in the posterior superior temporal gyms (STG) showed a larger local advantage than controls if the lesion was on the right and a global advantage if the lesion was on the left. STG patients were no more influenced by visual angle than were controls. Control subjects also showed the usual interference of global distractors on responding to local targets. STG patients showed little evidence of interference. Control patients with lesions centered in the rostral inferior parietal lobe performed normally. The findings suggest that several component mechanisms are involved in the processing of hierarchical levels of structure, each linked to specific anatomical regions.
Psychophysiology of movement related brain potentials: task dependence and neural generators
Authors:
Jaswinder Singh
David L. Woods
Robert T. Knight
Date: 1990
Prefrontal cortex gating of auditory transmission in humans
Abstract:
Middle-latency auditory evoked potentials (MAEPs) were recorded in controls and patients with focal lesions in dorsolateral prefrontal cortex. Unilateral prefrontal lesions increased the amplitude of the Pa component of the MAEP beginning at 25-35 ms poststimulus. The data suggest that prefrontal cortex exerts early inhibitory modulation of input to primary auditory cortex in humans.
Auditory Evoked Potentials from the primary auditory cortex of the cat: topographic and pharmacological studies
Abstract:
Wave VI (8.4 msec) of the brain-stem auditory evoked potential (BAEP) was maximal in a discrete region of primary auditory cortex (AI) of the anesthetized cat. Wave VI underwent rapid amplitude decrease over millimeter distances in the AI region and followed high stimulation rates. Wave VI did not show intracortical polarity inversion nor was it abolished by epicortical or intracortical GABA administration. The data are compatible with a wave VI source in the terminal axons of the thalamo-cortical radiations. Middle latency auditory responses (MAEPs) generated 10-40 msec after auditory stimulation were also recorded in a circumscribed area of AI. In contrast to wave VI, these primary auditory cortex potentials (Pa 18.3 msec; Nb 31.9 msec) underwent transcortical polarity inversion, correlated with intracortical multi-unit activity in the AI region and were reversibly altered or abolished by epicortical or intracortical GABA administration to the AI region. The data suggest that the Pa and Nb components of the cat MAEP are intracortically generated by neuronal elements in the AI region.
Pre-movement parietal lobe input to human sensorimotor cortex
Abstract:
Movement-related cortical potentials (MRPs) were recorded in an auditory dichotic selective attention experiment in patients with focal lesions centered in either posterior superior temporal gyrus (temporal) or in lateral parietal cortex (parietal). Controls and temporal patients generated comparable pre-movement negative shifts (NSs) and motor potentials (MPs), onsetting about 400 ms prior to movement and maximal in amplitude over scalp sites contralateral to button press. Unilateral parietal cortex lesions markedly reduced the NSs but preserved the MP component of the MRP. The results indicate that human parietal association cortex exerts modulatory input to sensorimotor cortex, beginning at least 400 ms prior to movement. The differential effect on the NSs and MPs by parietal lesions suggests that these MRP components may have independent intracranial generators.
Contributions of temporal-parietal junction to the human auditory P3
Abstract:
The P3 component of the event-related potential (ERP) is generated in humans and other mammalian species when attention is drawn to infrequent stimuli. We assessed the role of subregions of human posterior association cortex in auditory P3 generation in groups of patients with focal cortical lesions. Auditory P3s were recorded to target (P3b) and unexpected novel stimuli (P3a) in monaural and dichotic signal detection experiments. Two groups of patients were studied with lesions of: (1) temporal-parietal junction including posterior superior temporal plane and adjacent caudal inferior parietal cortex; and (2) the lateral parietal lobe including the rostral inferior parietal lobe and portions of superior parietal lobe. Extensive lateral parietal cortex lesions had no effect on the P3. In contrast, discrete unilateral lesions centered in the posterior superior temporal plane eliminated both the auditory P3b and P3a at electrodes over the posterior scalp. The results indicate that auditory association cortex in the human temporal-parietal junction is critical for auditory P3 generation.