Biomedical subjects

Jochen Kaiser

Publications and source records attributed to Jochen Kaiser.

18 recordsLinked to original sources

PubMed2005

Human gamma-band activity: a window to cognitive processing.

This review highlights recent developments in research on human cortical oscillations in the gamma-band range (30-100 Hz). Electroencephalography has demonstrated a role of these signals for cognitive functions including visual perception, attention, learning and memory. During auditory processing, magnetoencephalogram has identified oscillatory activity in higher frequency ranges and with a more discrete localization than electroencephalogram. Gamma-band activity increases have been observed in the putative auditory dorsal and ventral processing streams during the processing of auditory spatial and pattern information, respectively. Additional gamma-band activity has been found over the frontal cortex during top-down tasks. Oscillatory activity in the gamma range may serve to assess the temporal dynamics of cortical networks and their interactions.

Biological Clocks↗

PubMed2005

Cortical oscillatory activity during spatial echoic memory.

In human magnetoencephalogram, we have found gamma-band activity (GBA), a putative measure of cortical network synchronization, during both bottom-up and top-down auditory processing. When sound positions had to be retained in short-term memory for 800 ms, enhanced GBA was detected over posterior parietal cortex, possibly reflecting the activation of higher sensory storage systems along the hypothesized auditory dorsal space processing stream. Additional prefrontal GBA increases suggested an involvement of central executive networks in stimulus maintenance. The present study assessed spatial echoic memory with the same stimuli but a shorter memorization interval of 200 ms. Statistical probability mapping revealed posterior parietal GBA increases at 80 Hz near the end of the memory phase and both gamma and theta enhancements in response to the test stimulus. In contrast to the previous short-term memory study, no prefrontal gamma or theta enhancements were detected. This suggests that spatial echoic memory is performed by networks along the putative auditory dorsal stream, without requiring an involvement of prefrontal executive regions.

Acoustic Stimulation↗

PubMed2004

Frontal gamma-band activity in magnetoencephalogram during auditory oddball processing.

Previous studies have demonstrated induced gamma-band activity (GBA) over posterior temporo-parietal and inferior frontal cortex during auditory spatial vs pattern mismatch processing, respectively. Here we investigated magnetoencephalographic oscillatory responses during an active auditory pattern oddball task. Fourteen subjects were instructed to detect pairs of deviating animal vocalizations in a sequence of standard sounds. The comparison of targets with standards revealed differences in oscillatory activity >80 Hz 200-300 ms after stimulus onset. GBA was increased over left inferior frontal cortex, replicating previous results of putative auditory ventral stream activation during passive pattern deviance processing. Additional GBA enhancements over superior frontal cortex were specific to active target detection. They probably reflected executive networks involved in memory maintenance and decision making.

Acoustic Stimulation↗

PubMed2004

Hearing lips: gamma-band activity during audiovisual speech perception.

Auditory pattern changes have been shown to elicit increases in magnetoencephalographic gamma-band activity (GBA) over left inferior frontal cortex, forming part of the putative auditory ventral "what" processing stream. The present study employed a McGurk-type paradigm to assess whether GBA would be associated with subjectively perceived changes even when auditory stimuli remain unchanged. Magnetoencephalograms were recorded in 16 human subjects during audiovisual mismatch perception. Both infrequent visual (auditory /ta/ + visual /pa/) and acoustic deviants (auditory/pa/ + visual /ta/) were compared with frequent audiovisual standards (auditory /ta/ and visual /ta/). Statistical probability mapping revealed spectral amplitude increases at approximately 75 and approximately 78 Hz to visual deviants. GBA to visual deviants peaked 160 ms after auditory stimulus onset over posterior parietal cortex, at 270 ms over occipital areas and at 320 ms over left inferior frontal cortex. The latter GBA enhancement was consistent with the increase observed previously to pure acoustic mismatch, supporting a role of left inferior frontal cortex for the representation of perceived auditory pattern change. The preceding gamma-band changes over posterior areas may reflect processing of incongruent lip movements in visual motion areas and back-projections to earlier visual cortex.

Adult↗

PubMed2004

Magnetoencephalographic gamma-band responses to illusory triangles in humans.

Electroencephalography studies have suggested that the perception of illusory figures is associated with increases in gamma-band activity putatively reflecting the formation of synchronously firing neuronal assemblies. Here we assessed magnetoencephalographic gamma-band activity, which has been shown to be topographically more focal than in electroencephalogram. In line with functional brain imaging findings, we hypothesized gamma-band activity over ventral visual stream areas. In addition, we expected that the analysis of oscillatory activity would provide information on the time courses and connectivity patterns of these activations. Following a paradigm previously assessed with electroencephalography, 16 adults were presented four types of stimuli at equal probabilities: illusory (Kanizsa) triangles, real triangles, no-triangle stimuli with rotated inducer disks, and curved illusory triangles serving as targets that subjects had to respond to. Induced oscillatory responses were compared between illusory triangles and no-triangle stimuli and between illusory and real triangles using a statistical probability mapping method. Illusory triangles were distinguished from no-triangles by increased activity at around 70 Hz over midline occipital cortex peaking at 240 ms after stimulus onset. This was followed by activations over bilateral lateral occipital areas at 430 ms. Illusory triangles differed from real triangles by increased spectral activity at 90 Hz over posterior parietal cortex between 100 and 450 ms after stimulus onset, suggesting an involvement of visual dorsal stream regions. Coherence analysis showed increased connectivity between posterior parietal and lateral occipital cortex. These findings suggest that illusory triangles are encoded in parallel by networks along the visual ventral and dorsal streams.

Adult↗

PubMed2003

Conscious perception of brain states: mental strategies for brain-computer communication.

Direct brain-computer communication utilises self-regulation of brain potentials to select letters, words or symbols from a computer menu. In this study a completely paralysed (locked-in) patient learnt to produce slow cortical potential (SCP) shifts to operate a binary spelling device. After hundreds of training sessions he gave a detailed description of his mental strategies for self-regulation. His cognitive strategies matched with the electrocortical changes perfectly. Thus he produced a contingent negative variation (CNV) with images of preparation such as an arrow being drawn on a bow. To produce a positive potential shift he imagined the arrow shooting up from the bow. To suppress potential shifts he tried to stop thinking. The study demonstrates that patients become sensitive for their brain states with increasing self-regulation practice. The use of conscious cognitive strategies may, however, be incompatible with the complete automatization of the self-regulation skill.

Amyotrophic Lateral Sclerosis↗

PubMed2003

Memory-related EEG power and coherence reductions in mild Alzheimer's disease.

OBJECTIVES: To examine memory-related EEG power and coherence over temporal and central recording sites in patients with early Alzheimer's disease (AD) and normal controls. METHOD: EEG was recorded from central (Fz, Cz and Pz) and temporal (T3 and T4) electrodes while ten very mild AD patients and ten controls performed a Sternberg-type memory scanning task with three levels of working memory load. Spectral power in delta (0-3 Hz), theta (3-5 Hz), lower alpha1 (5-7 Hz), lower alpha2 (7-9 Hz), upper alpha (9-11 Hz) and beta (15-30 Hz) was averaged for temporal and central electrodes. Coherence was averaged between central electrodes, between central and right temporal electrodes and between central and left temporal electrodes. RESULTS: While behavioral performance of very mild AD patients did not differ significantly from that of normal controls, findings suggest that normal controls but not AD patients respond to memory demands by increasing upper alpha power over temporal cortex. When compared with normal controls, AD patients had reduced upper alpha coherence between central and right temporal cortex. DISCUSSION: Results are consistent with previous research on the role of upper alpha in semantic memory and suggest that very mild AD may inhibit selective synchronization of upper alpha in temporal lobes. Reduced coherence between central and temporal cortex is discussed in light of a neurological model of AD that hypothesizes reduced electrocortical efficiency and a breakdown of neural network communication to temporal lobes possibly resulting from temporal lobe atrophy.

Aged↗

PubMed2003

Electrocortical and behavioral effects of chronic immobility on word processing.

Neuroelectrical and subjective effects of chronic motor deficits (severe immobility) on word processing were explored. A total of ten artificially ventilated patients with end-stage amyotrophic lateral sclerosis (ALS), seven patients with tetraplegia due to a high spinal cord injury (SCI), and nine matched controls were examined. Both ALS and SCI patients were almost completely paralyzed; eye, head, and face movements were intact in SCI but not in ALS patients. Event-related brain potentials (ERPs) were recorded during presentation of verbs with strong motor-action associations and nouns with strong visual associations. Subjects estimated the subjective strength of motor and visual associations for each word using a scale from 0 to 5. No between-group difference was found for subjectively rated motor associations. All patients reported much stronger visual associations for both nouns and verbs than healthy subjects. ERPs to both word classes revealed a left occipital negativity in SCI patients at a latency of 200-300 ms, and a marked decrease of the slow positive wave in the interval of 300-800 ms in the two patient groups. Both psychophysical and electrophysiological data suggest compensatory activation of visual information processing areas in severely paralyzed patients. The more pronounced effects in the SCI group as compared with the ALS group may be attributed to somatosensory deafferentation in SCI patients, while the sensory inflow in ALS remains relatively intact.

Adult↗

PubMed2003

Dynamics of sensorimotor cortex activation to spatial sounds precueing ipsi- versus contralateral manual responses.

Spatially informative visual precues give rise to event-related potential asymmetries with higher negativities over the contralateral hemisphere. However the attribution of these potentials to sensorimotor areas is still unclear. The present magnetoencephalography study assessed movement preparation processes to auditory spatial precues. Event-related desynchronization (ERD) was measured to test the hypothesis that lateralized sounds would give rise to a fast, stimulus-driven activation of motor networks independent of the precued response side. The lateralized vowels /a/ and /e/ served as precues for either ipsi- or contralateral responses, respectively, which had to be executed when an imperative stimulus was presented 1 s after precue onset. Two separate experiments were conducted with either blocked or mixed presentation of ipsi- and contralateral precues. Beta ERD over sensorimotor regions representing the stimulus side was elicited by both types of precues approximately 200 ms after their onset. For contralateral precues, a switch of beta ERD to the response hemisphere took place approximately 400 ms after trial-onset, peaking prior to the imperative stimulus (approximately 800 ms post trial-onset). Signal subspace projection demonstrated a high topographical correspondence between the early precue-related ERD and the pattern immediately preceding the response, suggesting that both were generated in similar motor networks. Apparently lateralized sounds give rise to an early activation of contralateral motor networks independent of the precued response. This suggests strong associations between space processing and action preparation networks, with fast activations preceding a detailed cortical analysis of stimulus meaning.

Adult↗

PubMed2003

Dynamics of working memory for moving sounds: an event-related potential and scalp current density study.

Human brain imaging studies have suggested that posterior temporo-parietal regions are involved in auditory spatial processing. We used electroencephalography to investigate the dynamics of temporo-parietal networks during working memory for moving sounds. A delayed matching-to-sample task required a decision on the identity of positions and trajectories of two moving sounds S1 and S2 presented with delays of 927 or 1427 ms. Moving sounds consisted of noise bursts positioned at successive angles to create the impression of one of six possible trajectories at variable spatial positions. Stimuli in the equally difficult control condition were identical to the memory task up to S2, which was replaced by a spatial displacement in the otherwise stationary background sound whose direction had to be detected. Event-related potentials were recorded from 31 scalp electrodes in 15 subjects. Scalp current density estimates allowed to identify the following components. The fronto-central negative variation preceding S2 did not differ between tasks. In contrast, the sustained negative current during the presentation of S1 originating from superior temporal cortex was more pronounced for the memory task, probably reflecting enhanced attention allocation and foreground-background discrimination. Most importantly, the memory task activated current sources over bilateral posterior parietal regions between the middle of S1 and the end of the delay phase. This component was completely absent in the control condition. In summary, the present study disclosed varying degrees of memorization-related, top-down driven influences on the processing of moving sounds at different stages of an auditory network involving temporal and parietal regions.

Acoustic Stimulation↗

PubMed2003

Dynamics of gamma-band activity in human magnetoencephalogram during auditory pattern working memory.

Both electrophysiological research in animals and human brain imaging studies have suggested that, similar to the visual system, separate cortical ventral "what" and dorsal "where" processing streams may also exist in the auditory domain. Recently we have shown enhanced gamma-band activity (GBA) over posterior parietal cortex belonging to the putative auditory dorsal pathway during a sound location working memory task. Using a similar methodological approach, the present study assessed whether GBA would be increased over auditory ventral stream areas during an auditory pattern memory task. Whole-head magnetoencephalogram was recorded from N = 12 subjects while they performed a working memory task requiring same-different judgments about pairs of syllables S1 and S2 presented with 0.8-s delays. S1 and S2 could differ either in voice onset time or in formant structure. This was compared with a control task involving the detection of possible spatial displacements in the background sound presented instead of S2. Under the memory condition, induced GBA was enhanced over left inferior frontal/anterior temporal regions during the delay phase and in response to S2 and over prefrontal cortex at the end of the delay period. gamma-Band coherence between left frontotemporal and prefrontal sensors was increased throughout the delay period of the memory task. In summary, the memorization of syllables was associated with synchronously oscillating networks both in frontotemporal cortex, supporting a role of these areas as parts of the putative auditory ventral stream, and in prefrontal, possible executive regions. Moreover, corticocortical connectivity was increased between these structures.

Acoustic Stimulation↗

PubMed2003

A brain-computer interface (BCI) for the locked-in: comparison of different EEG classifications for the thought translation device.

OBJECTIVE: The Thought Translation Device (TTD) for brain-computer interaction was developed to enable totally paralyzed patients to communicate. Patients learn to regulate slow cortical potentials (SCPs) voluntarily with feedback training to select letters. This study reports the comparison of different methods of electroencephalographic (EEG) analysis to improve spelling accuracy with the TTD on a data set of 6,650 trials of a severely paralyzed patient. METHODS: Selections of letters occurred by exceeding a certain SCP amplitude threshold. To enhance the patient's control of an additional event-related cortical potential, a filter with two filter characteristics ('mixed filter') was developed and applied on-line. To improve performance off-line the criterion for threshold-related decisions was varied. Different types of discriminant analysis were applied to the EEG data set as well as on wavelet transformed EEG data. RESULTS: The mixed filter condition increased the patients' performance on-line compared to the SCP filter alone. A threshold, based on the ratio between required selections and rejections, resulted in a further improvement off-line. Discriminant analysis of both time-series SCP data and wavelet transformed data increased the patient's correct response rate off-line. CONCLUSIONS: It is possible to communicate with event-related potentials using the mixed filter feedback method. As wavelet transformed data cannot be fed back on-line before the end of a trial, they are applicable only if immediate feedback is not necessary for a brain-computer interface (BCI). For future BCIs, wavelet transformed data should serve for BCIs without immediate feedback. A stepwise wavelet transformation would even allow immediate feedback.

Communication Devices for People with Disabilities↗

PubMed2003

Neurofeedback treatment for attention-deficit/hyperactivity disorder in children: a comparison with methylphenidate.

Clinical trials have suggested that neurofeedback may be efficient in treating attention-deficit/hyperactivity disorder (ADHD). We compared the effects of a 3-month electroencephalographic feedback program providing reinforcement contingent on the production of cortical sensorimotor rhythm (12-15 Hz) and betal activity (15-18 Hz) with stimulant medication. Participants were N = 34 children aged 8-12 years, 22 of which were assigned to the neurofeedback group and 12 to the methylphenidate group according to their parents' preference. Both neurofeedback and methylphenidate were associated with improvements on all subscales of the Test of Variables of Attention, and on the speed and accuracy measures of the d2 Attention Endurance Test. Furthermore, behaviors related to the disorder were rated as significantly reduced in both groups by both teachers and parents on the IOWA-Conners Behavior Rating Scale. These findings suggest that neurofeedback was efficient in improving some of the behavioral concomitants of ADHD in children whose parents favored a nonpharmacological treatment.

Attention Deficit Disorder with Hyperactivity↗

PubMed2003

Induced gamma-band activity and human brain function.

Oscillatory activity in the gamma-band range has been related both to gestalt perception and to cognitive functions such as attention, learning, and memory. After giving a brief account of recent findings from electroencephalography and intracortical recordings, the present review will focus on spectral activity in the magnetoencephalogram. Here, gamma-band effects are topographically more local and involve higher frequencies than in the electroencephalogram. Bottom-up-driven auditory spatial mismatch detection elicits gamma-band activity over posterior parietal cortex, whereas auditory pattern mismatch processing leads to gamma-band enhancements over anterior temporal and inferior frontal regions. These topographies support representations of auditory spatial and pattern information in the putative dual auditory "where" and "what" pathways, respectively. During top-down-guided auditory spatial and pattern-working memory tasks, prefrontal gamma-band increases are observed in addition to activations over putative auditory stream areas. Moreover, stimulus maintenance in working memory is accompanied by coherence increases between sensory and prefrontal regions. Gamma-band topographies in magnetoencephalogram are highly comparable with hemodynamic brain imaging studies but yield additional information on the temporal dynamics of activations and connectivity patterns. In summary, magnetoencephalographic gamma-band activity revealed both local synchronization patterns and cortico-cortical interactions accompanying cognitive processes at a good spatial and high temporal resolution.

Animals↗

PubMed2002

Dynamics of gamma-band activity during an audiospatial working memory task in humans.

The representation of visual objects in short-term memory has been shown to be related to increased gamma-band activity in the electroencephalogram. Using a similar paradigm, we investigated oscillatory magnetoencephalographic activity in human subjects during a delayed matching-to-sample task requiring working memory of auditory spatial information. The memory task involved same-different judgments about the lateralization angle of pairs of filtered noise stimuli (S1 and S2) separated by 800 msec delays of background noise. This was compared with a control condition requiring the detection of a possible change in the background noise volume appearing instead of S2 (volume task). Statistical probability mapping revealed increased spectral activity at 59 Hz over left parietal cortex during the delay phase of the memory condition. In addition, 59 Hz coherence was enhanced between left parietal and right frontal sensors. During the end of the delay and during the presentation of S2, enhanced gamma-band activity at 67 Hz was observed over right frontal and later over midline parietal areas. In contrast, the volume task was characterized by increased left inferior frontotemporal 59 Hz spectral amplitude after S1. Apparently representation of the spatial position of a sound source is associated both with synchronization of networks in parietal areas involved in the auditory dorsal stream and with increased coupling between networks serving representation of audiospatial information and frontal executive systems. The comparison with S2 seemed to activate frontal and parietal neuronal ensembles. Gamma-band activity during the volume task may reflect auditory pattern encoding in auditory ventral stream areas.

Adult↗

PubMed2002

Magnetic oscillatory responses to lateralization changes of natural and artificial sounds in humans.

Oscillatory signals in human magnetoencephalogram were investigated as correlates of cortical network activity in response to sound lateralization changes. Previously, we found lateralized presentations of a monosyllabic word to elicit posterior temporo-parietal gamma-band activity, possibly reflecting synchronization of neuronal assemblies in putative auditory dorsal stream areas. In addition, beta activity was decreased over sensorimotor regions, suggesting the activation of motor networks involved in orientating. The present study investigated responses to lateralization changes of both a barking dog sound and a distorted noise to test whether beta desynchronization would depend on the sound's relevance for orientating. Eighteen adults listened passively to 900 samples of each sound in separate location mismatch paradigms with midline standards and both right- and left-lateralized deviants. Lateralized distorted noises were accompanied by enhanced spectral amplitude at 58-73 Hz over right temporo-parietal cortex. Left-lateralized barking dog sounds elicited right and right-lateralized sounds elicited bilateral temporo-parietal spectral amplitude increases at approximately 77 Hz. This replicated the involvement of posterior temporo-parietal areas in auditory spatial processing. Only barking dog sounds, but not distorted noises, gave rise to 30 Hz desynchronization over contralateral sensorimotor areas, parieto-frontal gamma coherence increases and beta coherence reductions between sensorimotor and prefrontal sensors. Apparently passive listening to lateralized natural sounds with a potential biological relevance led to an activation of motor networks involved in the automatic preparation for orientating. Parieto-frontal coherence increases may reflect enhanced coupling of networks involved in the integration of auditory spatial and motor processes.

Acoustic Stimulation↗

PubMed2002

A non-invasive communication device for the paralyzed.

An EEG-based communication system has been developed to re-establish communication in severely paralyzed patients who operate the device by generating shifts of their slow cortical potentials. Training to gain control over slow cortical potentials was based on visual feedback and operant conditioning strategies. The vertical movement of a graphic signal on a computer screen informs the patients about the course of their slow cortical potential amplitude. Positive slow cortical potential shifts move the cursor up, negative shifts move it down. These shifts are then translated into binary responses. When a patient has achieved reliable control over his/her slow cortical potential shifts, these responses can be used to select or reject items presented at the bottom of the screen. As learning processes and applications differ considerably between patients, the present paper describes the data from one patient with amyotrophic lateral sclerosis. After about three months of training, this patient gained stable, near-perfect control over his slow cortical potentials. This skill enabled him to operate a specially designed program to communicate messages to his caregivers.

Adult↗

PubMed2002

Dynamics of gamma-band activity induced by auditory pattern changes in humans.

Increasing evidence suggests separate auditory pattern and space processing streams. The present paper describes two magnetoencephalogram studies examining gamma-band activity to changes in auditory patterns using consonant-vowel syllables (experiment 1), animal vocalizations and artificial noises (experiment 2). Two samples of each sound type were presented to passively listening subjects in separate oddball paradigms with 80% standards and 20% deviants differing in their spectral composition. Evoked magnetic mismatch fields peaking approximately 190 ms poststimulus showed a trend for a left-hemisphere advantage for syllables, but no hemispheric differences for the other sounds. Frequency analysis and statistical probability mapping of the differences between deviants and standards revealed increased gamma-band activity above 60 Hz over left anterior temporal/ventrolateral prefrontal cortex for all three types of stimuli. This activity peaked simultaneously with the mismatch responses for animal sounds (180 ms) but was delayed for noises (260 ms) and syllables (320 ms). Our results support the hypothesized role of anterior temporal/ventral prefrontal regions in the processing of auditory pattern change. They extend earlier findings of gamma-band activity over posterior parieto-temporal cortex during auditory spatial processing that supported the putative auditory dorsal stream. Furthermore, earlier gamma-band responses to animal vocalizations may suggest faster processing of fear-relevant information.

Adult↗