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Matthias M Müller

Publications and source records attributed to Matthias M Müller.

At least 19 recordsLinked to original sources
PubMed2007

Sustained division of spatial attention to multiple locations within one hemifield.

Attending to a location in space significantly improves stimulus perception at that location. Everyday experience requires the deployment of attention to multiple objects at different locations. Recent empirical evidence suggests that the "beam" of attention can be divided between non-contiguous areas of the visual field. Whether this is only possible when stimuli are presented in different hemifields and harder, if not impossible, when stimuli are in the same hemifield is an ongoing debate. Here we use an electrophysiological measure of sustained attentional resource allocation (the steady-state visual evoked potential, SSVEP) to address this question. In combination with behavioural data we demonstrate that splitting the attentional "beam" is in principle possible within one hemifield. However, results showed that task performance was in general lower for same-hemifield presentation as opposed to our previous study with different-hemifield presentation [M.M. Müller, P. Malinowski, T. Gruber, S.A. Hillyard, Sustained division of the attentional spotlight, Nature 424 (2003) 309-312]. SSVEP amplitude showed a mixed pattern of results for stimuli presented in the upper versus lower quadrant of the left visual hemifield under conditions of attending to two separated locations. Results are discussed in the light of the bilateral distribution advantage hypothesis and differences in stimulus salience between the upper and lower visual field.

Adult↗
PubMed2006

A cross-laboratory study of event-related gamma activity in a standard object recognition paradigm.

This study proposes a standard paradigm for the investigation of visual information processing by means of gamma activity and presents a novel set of stimuli with a broad range of complex, coloured familiar real world and unfamiliar nonsense objects which are well matched with respect to physical stimulus properties. In order to demonstrate that the paradigm and stimulus set yield reliable results both were employed in two electrophysiological investigations in two independent laboratories. Participants were required to discriminate familiar from unfamiliar stimuli. The pattern of results was very consistent across laboratories. Early event-related potentials were not influenced by the stimulus type suggesting that physical stimulus properties did not confound object familiarity. Induced gamma band activity was stronger for familiar than for unfamiliar objects, supporting the notion of gamma activity as a signature of cortical networks underlying object representations.

Adult↗
PubMed2006

Oscillatory brain activity in the human EEG during indirect and direct memory tasks.

Up to today, the neuronal bases of activating and establishing a memory trace are not well understood. Several findings point towards the idea that the activation of an engram is mirrored in induced oscillatory bursts in the gamma frequency range (> 20 Hz; induced gamma band responses; iGBRs). In the present study, we further investigated this hypothesis. Volunteers performed two tasks on repeated pictures of familiar and unfamiliar objects. They either made a familiarity decision with repetition being task irrelevant (indirect memory task), or a recognition judgment with repetition being task relevant (direct memory task). Furthermore, we complemented iGBR analyses by investigating other brain responses known to be modulated by mnemonic manipulations, namely, evoked gamma oscillations, lower frequency oscillations, and event-related potentials (ERPs). The results obtained for the indirect task replicated previous findings of repetition suppression of iGBRs for repeated familiar stimuli and an increase of iGBRs for repeated unfamiliar objects. These effects might be linked to the 'sharpening' of a cell assembly representing a familiar object and to the formation of a new object representation for unfamiliar stimuli, respectively. In contrast, the direct task revealed no repetition-related modulations of iGBRs. Thus, modulations of iGBRs are not a mere automatic consequence of repeated stimulus processing but might rather mirror changes within cortical object representation according to use-dependent plasticity principles. Furthermore, evoked gamma responses, lower frequency bands, and late components of the ERPs correlated with more specific subprocesses during mnemonic functioning.

Adult↗
PubMed2006

Repetition suppression of induced gamma band responses is eliminated by task switching.

The formation of cortical object representations requires the activation of cell assemblies, correlated by induced oscillatory bursts of activity > 20 Hz (induced gamma band responses; iGBRs). One marker of the functional dynamics within such cell assemblies is the suppression of iGBRs elicited by repeated stimuli. This effect is commonly interpreted as a signature of 'sharpening' processes within cell-assemblies, which are behaviourally mirrored in repetition priming effects. The present study investigates whether the sharpening of primed objects is an automatic consequence of repeated stimulus processing, or whether it depends on task demands. Participants performed either a 'living/non-living' or a 'bigger/smaller than a shoebox' classification on repeated pictures of everyday objects. We contrasted repetition-related iGBR effects after the same task was used for initial and repeated presentations (no-switch condition) with repetitions after a task-switch occurred (switch condition). Furthermore, we complemented iGBR analysis by examining other brain responses known to be modulated by repetition-related memory processes (evoked gamma oscillations and event-related potentials; ERPs). The results obtained for the 'no-switch' condition replicated previous findings of repetition suppression of iGBRs at 200-300 ms after stimulus onset. Source modelling showed that this effect was distributed over widespread cortical areas. By contrast, after a task-switch no iGBR suppression was found. We concluded that iGBRs reflect the sharpening of a cell assembly only within the same task. After a task switch the complete object representation is reactivated. The ERP (220-380 ms) revealed suppression effects independent of task demands in bilateral posterior areas and might indicate correlates of repetition priming in perceptual structures.

Adult↗
PubMed2005

Brain electrical tomography (BET) analysis of induced gamma band responses during a simple object recognition task.

The formation of cortical object representations requires the activation of cell assemblies, correlated by induced oscillatory bursts above 20 Hz (gamma band), which are characterized by trial-by-trial latency fluctuations around a mean of approximately 300 ms after stimulus onset. The present electroencephalogram (EEG) study was intended to uncover to the generators of induced gamma band responses (GBRs) and to analyze phase-synchronization between these sources. A standard object recognition task was used to elicit gamma activity. At the scalp surface (electrode space), we found an augmentation of induced GBRs after the presentation of meaningful (familiar) as opposed to meaningless (unfamiliar) stimuli, which was accompanied by a dense pattern of significant phase-locking values between distant recording sites. Subsequently, intracranial current density distributions compatible with the observed scalp voltage topographies were estimated by means of VARETA (Variable Resolution Electromagnetic Tomography). In source space brain electrical tomographies (BETs) revealed widespread generators of induced GBRs at temporal, parietal, posterior, and frontal areas. Phase-locking analysis was calculated between re-constructed electrode signals based on separate forward solutions of the observed generators, thereby eliminating the possibly confounding influence of activity from areas not under observation. The results support the view that induced GBRs signify synchronous neuronal activity in a broadly distributed network during object recognition. The localization of the generators of event-related potentials (ERPs), evoked gamma activity, and induced alpha activity revealed different sources as compared to the induced GBR and, thus, seem to mirror complementary functions during the present task as compared to induced high-frequency brain dynamics.

Adult↗
PubMed2004

Induced gamma band responses: an early marker of memory encoding and retrieval.

Although mnemonic processes have been widely studied using event-related potentials (ERPs), memory-related oscillatory changes in the EEG have been relatively neglected. The aim of this study was to investigate memory encoding- and retrieval-related changes in the frequency domain. In particular, we focused on induced gamma band responses (GBRs), which are a candidate for the establishment and activation of widespread cell assemblies. At encoding, results revealed increased GBRs for subsequently recognised relative to subsequently forgotten items. At retrieval, recognised old stimuli were associated with higher GBRs compared to new stimuli. During encoding and retrieval GBR modulation preceded that of ERPs. Thus, GBRs might be a correlate of processes that onset earlier to those responsible for memory encoding and retrieval ERP effects.

Adolescent↗
PubMed2004

Oscillatory brain activity dissociates between associative stimulus content in a repetition priming task in the human EEG.

The retrieval and formation of cortical object representations seem to require the activation of neuronal cell assemblies, correlated by synchronized neuronal activity in the gamma band range (>20 Hz). In the present electroencephalogram (EEG) study we have analysed induced gamma band activity during the repetition of familiar (meaningful) and unfamiliar (meaningless) line drawings. Results showed a broad posterior distribution of induced gamma band responses (GBRs) after the initial presentation of a familiar stimulus. Repeated presentations of the same picture resulted in a decrease of GBRs, accompanied by a decrease in the number of electrode pairs exhibiting significant phase-locking values. These effects might be linked to a 'sharpening' mechanism within a cell assembly representing a familiar object. In contrast, the re-presentation of primed unfamiliar stimuli was associated with an augmentation of gamma power and an increase in significantly phase-locked pairs of electrodes. These findings might be a signature of the formation of a new cortical network representing an object. Event related potentials (ERPs) showed a decrease in amplitude independent of the stimuli's associative content, and, thus, seem to play a complementary role in repetition priming as compared to high-frequency brain dynamics.

Adult↗
PubMed2004

Selective spatial attention to left or right hand flutter sensation modulates the steady-state somatosensory evoked potential.

Steady-state somatosensory evoked potentials (SSSEPs) were recorded from the scalp of human subjects elicited by 20 and 26 Hz mechanical vibrations applied simultaneously to the index finger of the left (20 Hz) and right hand (26 Hz). Subjects were instructed to attend to the flutter vibration at one finger while ignoring the other finger and to detect rare target events at the to-be-attended finger. The amplitude of the frequency coded SSSEP elicited by the attended vibration was significantly enlarged when attention was focused at the respective finger. This amplitude enhancement with attention was most prominent over fronto-central electrode locations contralateral to the attended finger. This is the first report to show the attentional modulation of the SSSEP amplitude in humans, suggesting an enhancement of neural responses in the sense of flutter with attention. The findings will open a new approach for studying the neural mechanisms of sustained selective attention in somatosensation.

Adult↗
PubMed2004

Attentional modulation of the human somatosensory evoked potential in a trial-by-trial spatial cueing and sustained spatial attention task measured with high density 128 channels EEG.

We investigated the modulation of the somatosensory evoked potential (SEP) elicited by mechanical stimuli in a spatial sustained attention and a spatial trial-by-trial cueing design by means of high density electrode array EEG recordings. Subjects were instructed to detect rare tactile target stimuli at the to-be-attended hand while ignoring stimuli at the other hand. Analysis of the SEP revealed a highly complex pattern of results. The P50 component was significantly increased for attended stimuli in the sustained attention as opposed to the trial-by-trial cueing condition. However, no difference in amplitude was found for attended as opposed to unattended stimuli. High density electrode array recordings revealed a centero-frontal N140 component (N140c), which preceded the parietal N140 (N140p) by about 20 ms. The N140c exhibited an attention effect in particular in the trial-by-trial spatial cueing condition. The N140p was significantly enlarged with attention across both experimental conditions, but a closer inspection demonstrated that this was mainly due to the great attention effect in the trial-by-trial spatial cueing condition. The late positive component (190-380 ms after stimulus onset) exhibited a significant attention effect in both experimental conditions. The present experiment provides evidence that the attentional modulation of the SEP is different when tactile as opposed to electrical stimuli were used and when only somatosensory stimuli are presented with no further sensory stimulation in other modalities. Furthermore, transient as opposed to sustained spatial attention affected various components of the SEP in a different way.

Adult↗
PubMed2004

Effect of NIH-IV prostatitis on free and free-to-total PSA.

OBJECTIVE: To examine the effect of asymptomatic prostatic inflammation (NIH category IV prostatitis) on total PSA (tPSA), free serum PSA (fPSA) and the ratio of free-to-total prostate specific antigen (%fPSA). The role of free and %fPSA as a diagnostic tool for distinguishing between cancer and non-malignant diseases of the prostate was also investigated. MATERIAL AND METHODS: In a retrospective study 1090 prostate biopsies performed between January 2000 and September 2003 were evaluated and the levels of serum total and free PSA as well as the f/tPSA ratio were determined in samples obtained immediately before biopsy. 404 patients with full clinical and histological records were included in the study. All patients underwent 6 or 8 core primary prostate needle biopsies. RESULTS: A total of 404 patients were included in the analysis. 100 prostate cancer (PCa) (24.8%), 137 NIH-IV prostatitis (33.9%) and 143 patients with benign prostatic hyperplasias (BPH) (35.4%) were identified. 24 (5.9%) patients presented with both PCa and prostatitis on histology and were excluded from further analysis. The mean (median) levels of tPSA, fPSA and %fPSA were 11.94 ng/ml (8.0), 1.31 ng/ml (1.07) and 0.15 (0.14) for NIH-IV prostatitis; 11.94 ng/ml (8.35), 1.54 ng/ml and 0.13 (0.11) for prostate cancer; and 8.19 ng/ml (7.0), 1.48 ng/ml (1.03) and 0.18 (0.15) for BPH. No significant difference was found in tPSA levels between PCa and prostatitis (p = 0.32), while the difference in tPSA levels between PCa and BPH was significant (p = 0.007). Free PSA alone had no diagnostic power in distinguishing PCa from prostatitis (p = 0. 37) and BPH (p = 0. 61). By contrast, the f/tPSA ratio showed significant between-group differences (PCa versus prostatitis (p = 0. 011), PCa versus BPH (p = 0.0001). CONCLUSIONS: Chronic asymptomatic prostatitis NIH category IV has similar effects on total PSA and free PSA levels in serum as PCa. fPSA alone cannot distinguish prostate cancer from non-malignant inflammatory disease of the prostate. The ratio of free-to-total PSA is significantly different in PCa and NIH category IV prostatitis.

Aged↗
PubMed2004

Modulation of oscillatory brain activity and evoked potentials in a repetition priming task in the human EEG.

Cortical object representations seem to require the formation of neural cell assemblies. The physiological correlate of cell assembly activity may be seen in synchronized neural activity in the gamma band range. The improvement in perceiving and identifying an object by experience is commonly referred to as repetition priming. One possible neural mechanism for repetition priming is 'repetition suppression' within a cell assembly coding the stimulus. The present electroencephalogram study was designed to investigate oscillatory brain activity when line drawings of concrete objects were repeated either immediately after a first presentation or after intervening a number of different stimuli. Results showed a broad posterior distribution of induced gamma band responses (GBRs) after the initial picture presentation. Repeated presentations of the same picture led to a significant decrease of induced gamma power. Furthermore, repeated presentations of the same object resulted in a decrease in phase synchrony between distant electrode sites. No significant repetition effects were found in the alpha or beta frequency range. The event-related potential (ERP), which was also modulated by priming, showed a different scalp distribution compared with induced GBRs. In addition, ERP repetition effects decayed at larger intervals between initial and repeated presentations, whereas induced GBRs were not modulated as a function of stimulus lag. We concluded that the decrease in amplitude of induced GBRs and the reduction of gamma phase synchrony between pairs of electrodes after repeated picture presentations might be linked to a 'sharpening' mechanism within a cell assembly representing an object.

Adult↗
PubMed2004

Neuronal synchronization and selective color processing in the human brain.

In the present study, subjects selectively attended to the color of checkerboards in a feature-based attention paradigm. Induced gamma band responses (GBRs), the induced alpha band, and the event-related potential (ERP) were analyzed to uncover neuronal dynamics during selective feature processing. Replicating previous ERP findings, the selection negativity (SN) with a latency of about 160 msec was extracted. Furthermore, and similarly to previous EEG studies, a gamma band peak in a time window between 290 and 380 msec was found. This peak had its major energy in the 55- to 70-Hz range and was significantly larger for the attended color. Contrary to previous human induced gamma band studies, a much earlier 40- to 50-Hz peak in a time window between 160 and 220 msec after stimulus onset and, thus, concurrently to the SN was prominent with significantly more energy for attended as opposed to unattended color. The induced alpha band (9.8-11.7 Hz), on the other hand, exhibited a marked suppression for attended color in a time window between 450 and 600 msec after stimulus onset. A comparison of the time course of the 40- to 50-Hz and 55- to 70-Hz induced GBR, the induced alpha band, and the ERP revealed temporal coincidences for changes in the morphology of these brain responses. Despite these similarities in the time domain, the cortical source configuration was found to discriminate between induced GBRs and the SN. Our results suggest that large-scale synchronous high-frequency brain activity as measured in the human GBR play a specific role in attentive processing of stimulus features.

Adult↗
PubMed2003

Effect of dexamethasone on voltage-gated K+ channels in Jurkat T-lymphocytes.

The voltage-gated K+ channel Kv1.3 is an important regulator of lymphocyte function. Activation of lymphocytes is accompanied by stimulation, whereas CD95-induced apoptosis by inhibition, of Kv1.3. The channel serves to maintain cell membrane potential, a prerequisite for signalling through the Ca2+ release-activated Ca2+ channel I(CRAC). As glucocorticoids are known to regulate lymphocyte function, the present study addressed the effect of dexamethasone on voltage-gated K+ channels in Jurkat T-lymphocytes. In whole-cell patch-clamp experiments current families evoked by 200-ms potential steps every 15 s from -70 mV to values from -120 to +100 mV revealed the functional expression of voltage-gated K+ channels. Pre-treatment of Jurkat T-lymphocytes for 2-3 h with 1 microM dexamethasone led to a significant decrease of voltage-gated K+ currents. Fura-2-fluorescence measurements showed that the readdition of Ca2+ to Ca(2+)-depleted cells led to a rapid increase of cytosolic Ca2+ activity. This increase of Ca2+ activity was blunted by both the K+ channel blocker margatoxin (10 nM) and 24 h pre-treatment with dexamethasone (1 microM). In conclusion, dexamethasone inhibits voltage-gated K+ channels in Jurkat T-lymphocytes, an effect impeding Ca2+ entry through I(CRAC).

Apoptosis↗
PubMed2003

Temporal stability of high-frequency brain oscillations in the human EEG.

Temporal stability of a given measurement within individual participants is a desirable property of psychophysiological measures. The present study aims to examine the reliability of high-frequency oscillatory activity in the human electroencephalogram (EEG) across 4 sessions. Convolution of the EEG time series with Morlet wavelets yielded time-frequency representations of the signal for each session. Stability of both topography and time course of gamma-band activity (GBA) was determined for two participants performing a feature-based selective attention task in four separate sessions, spaced at weekly intervals. We found high temporal stability of non-phase-locked GBA typically occurring in time ranges between 200 and 500 ms following presentation of a stimulus, both in terms of topography and time course. Early phase-locked GBA (80-120 ms) showed higher variability with respect to topography, but was consistent in terms of time course. We conclude that measures of high-frequency oscillatory activity as used in the cognitive neurosciences meet stability requirements necessary for meaningful interpretation of this parameter of brain function.

Adult↗
PubMed2003

Early modulation of visual perception by emotional arousal: evidence from steady-state visual evoked brain potentials.

Allocation of processing resources to emotional picture stimuli was examined using steady-state visual evoked brain potentials (ssVEPs). Participants viewed a set of 60 colored affective pictures from the International Affective Picture System, presented in a flickering mode at 10 Hz in order to elicit ssVEPs. Phase and amplitude of the 10-Hz ssVEP were examined for six picture categories: threat and mutilation (unpleasant), families and erotica (pleasant), and household objects and persons (neutral). Self-reported affective arousal and hedonic valence of the picture stimuli were assessed by means of subjective ratings. Viewing affectively arousing (unpleasant and pleasant) pictures was associated with enhanced ssVEP amplitude at parieto-occipital recording sites, as compared with neutral stimuli. Phase information suggested increased coactivation of right occipitotemporal and frontotemporal sources during processing of affectively arousing stimuli. These findings are consistent with reentrant modulation of early visual processing by distributed networks including subcortical and neocortical structures according to a stimulus's motivational relevance.

Adult↗
PubMed2002

Expansion of the tonotopic area in the auditory cortex of the blind.

A part of the core area of the auditory cortex was examined in nine blind and 10 sighted individuals by magnetic source imaging and was found to be enlarged by a factor of 1.8 in the blind compared with the sighted humans. Moreover, the latency of the N1m component of the auditory-evoked magnetic response was significantly decreased in the blind. The development of use-dependent cortical reorganization may be a consequence of the absence of visual input in combination with enhanced auditory activity generated by the long-term concentration by blind individuals on nonvisual cues to interact appropriately with the environment. It is consistent with and well suited to mediate the demonstrated increased ability of the blind to accurately localize acoustic sources in peripheral auditory fields and to decode speech.

Acoustic Stimulation↗
PubMed2002

Modulation of induced gamma band responses in a perceptual learning task in the human EEG.

Fragmented pictures of an object, which appear meaningless when seen for the first time, can easily be identified after the presentation of an unfragmented version of the same picture. The neuronal mechanism for such a rapid perceptual learning phenomenon is largely unknown. Recently, induced gamma band responses (GBRs) have been discussed as a possible physiological correlate of activity in cell assemblies formed by learning. The present study was designed to investigate the modulation of induced GBRs in a perceptual learning task by using a 128-channel EEG montage. In the first sequence of the experiment, fragmented pictures from the Snodgrass and Vandervart inventory were presented. The fragmentation of the pictures was selected that subjects were unable to identify them. In the second experimental sequence - the perceptual learning sequence - half of the pictures were displayed in their unfragmented version. In the third sequence, all pictures were presented again in the fragmented version. Now, subjects had to rate whether or not they could identify the images. Results showed an increase in spectral gamma power at parietal electrode sites for identified pictures. In addition, neural activity in the gamma band was highly synchronized between posterior electrodes. For pictures not presented in their complete version, we found no such pattern in the third sequence. From our results, we concluded that induced GBRs might represent a signature of synchronized neural activity in a Hebbian cell assembly, activated by the fragmented picture after perceptual learning took place. No difference between identified and unidentified pictures was found in the visual evoked potential in the same time range and in the evoked GBR in the same frequency range as the induced response.

Adult↗