Biomedical subjects

Jochen Kaiser

Publications and source records attributed to Jochen Kaiser.

25 records · Page 2Linked to original sources

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↗