Biomedical subjects

Hermann Ackermann

Publications and source records attributed to Hermann Ackermann.

33 records · Page 2Linked to original sources

PubMed2003

Processing of dynamic aspects of speech and non-speech stimuli: a whole-head magnetoencephalography study.

Clinical and experimental data indicate higher proficiency of the left hemisphere in encoding dynamic acoustic events such as rapid formant transitions (30-40 ms) that distinguish consonant-vowel syllables such as /ba/ or /da/. In order to further elucidate the underlying neurophysiological mechanisms, discrimination of /bi/-like formant transitions of variable duration (18, 36, 54, or 72 ms) from a steady-state /i/-like vowel was investigated by means of whole-head magnetoencephalography (MEG) both during visual distraction and selective attention. Voiced speech-like as well as unvoiced non-speech stimuli, matched for spectral envelope, served as test materials. Based on an oddball design, magnetic mismatch fields (MMF) were determined during an early (170-210 ms) and a late (230-290 ms) time window. Selective attention toward the deviant events resulted in enhanced MMFs particularly within the left hemisphere, indicating attention-dependent left-lateralized processing of dynamic auditory events across both the speech and non-speech domains. Perceptual discrimination improved along with transient lengthening. Accordingly, early MMF was, as a rule, enlarged in case of longer as compared to shorter transients. The 36-ms transitions yielded attention- and voicing-dependent deviations from the linear regression of MMF strength on transition duration. Considering the predominance of 30- to 40-ms formant transients across the world's languages, these findings indicate an adaptation or predisposition of the human perceptual system to the spectral/temporal characteristics of prototypical speech sounds. Signal voicing had no significant main effect on MMF strength despite superior perceptual performance in case of voiced as compared to voiceless target stimuli.

Acoustic Stimulation↗

PubMed2003

Parametric analysis of rate-dependent hemodynamic response functions of cortical and subcortical brain structures during auditorily cued finger tapping: a fMRI study.

A multitude of functional imaging studies revealed a mass activation effect at the level of the sensorimotor cortex during repetitive finger-tapping or finger-to-thumb opposition tasks in terms of either a stepwise or a monotonic relationship between movement rate and hemodynamic response. With respect to subcortical structures of the centralmotor system, there is, by contrast, some preliminary evidence for nonlinear rate/response functions within basal ganglia and cerebellum. To further specify these hemodynamic mechanisms, functional magnetic resonance imaging (fMRI) was performed during a finger-tapping task in response to acoustic stimuli (six different frequencies: 2.0, 2.5, 3.0, 4.0, 5.0 and 6.0 Hz; applied via headphones). Passive listening to the same auditory stimuli served as a control condition. Statistical evaluation of the obtained data considered two approaches: categorical and parametric analysis. As expected, the magnitude of the elicited hemodynamic response within left sensorimotor cortex (plateau phase at frequencies above 4 Hz) and mesiofrontal cortex paralleled movement rate. The observed bipartite mesial response pattern, most presumably, reflects functional compartmentalization of supplementary motor area (SMA) in a rostral component (pre-SMA) and in a caudal (SMA proper) component. At the level of the cerebellum, two significant hemodynamic responses within the hemisphere ipsilateral to the hand engaged into finger tapping (anterior/posterior quadrangular lobule and posterior quadrangular lobule) could be observed. Both activation foci exhibited a stepwise rate/response function. In accordance with clinical data, these data indicate different cerebellar contributions to motor control at frequencies below or above about 3 Hz, respectively. Caudate nucleus, putamen, and external pallidum of the left hemisphere displayed, by contrast, a negative linear rate/response relationship. The physiological significance of these latter findings remains to be clarified.

Adult↗

PubMed2003

Lasting amelioration of spatial neglect by treatment with neck muscle vibration even without concurrent training.

OBJECTIVE: It has been shown recently that neck muscle vibration in combination with an exploration training leads to lasting amelioration of spatial neglect. The present study evaluated whether vibration of the left posterior neck muscles alone has the potential to induce lasting reduction in spatial neglect. DESIGN: A multiple baseline design was used to control for spontaneous recovery or uncontrolled change caused by external events. PATIENTS: Six patients with spatial neglect following right hemisphere stroke. METHODS: Daily vibration treatment of the left posterior neck muscles for 20 minutes on 10 consecutive days. During vibration, patients did not perform any specific activities. RESULTS: We observed significant amelioration of spatial neglect after terminating the vibration therapy. The improvement was found to be stable at follow-up testing about 1.4 years later. CONCLUSION: Vibration of the left posterior neck muscles is a useful, non-invasive tool supplementing the established methods of spatial neglect treatment. It does not necessarily require the patient's co-operation, which is an important advantage especially in the early phases of rehabilitation.

Activities of Daily Living↗

PubMed2003

Relation between regional functional MRI activation and vascular reactivity to carbon dioxide during normal aging.

Recent blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging studies have shown a reduction of cerebral activation during aging, which may be associated with age-related changes of the cerebral vascular system. The authors used a global hypercapnic breath-holding challenge to define nonneuronal contributions to a significantly reduced activation in the primary sensorimotor cortex during finger tapping in a group of old (n = 6; mean age 65 years) compared with a group of young (n = 6; mean age 27 years) subjects. Within significantly activated voxels in both groups during finger tapping, the mean BOLD signal amplitudes were significantly smaller in the group of older subjects for both tasks. In those voxels showing significant activation only in young subjects during finger tapping, the response to hypercapnia was also greatly diminished in older subjects. The attenuated hypercapnic BOLD signal response in older subjects within this region suggests that age-dependent changes of the cerebral vasculature may alter the neuronal-vascular coupling. In older subjects, cerebral vessels may not react as effectively in response to a vasodilating stimulus, which will lead to differences in the number of voxels that pass a criterion threshold despite similar neuronal activation.

Adult↗

PubMed2002

The influence of critical bands on neuromagnetic fields evoked by speech stimuli in humans.

The various classes of speech sounds differ in their configuration of acoustic features. Vowels are characterized by specific local maxima of spectral energy distribution (formants). Using whole-head magnetoencephalography, the impact of variation of the first (F1) and second formant (F2) on the evoked N1m component (100 ms latency) was studied based on an oddball design. F1 changes yielded N1m enhancements in parallel to the spectral distance between standard and deviant stimuli. By contrast, F2 shifts gave rise to a non-linear relationship: the N1m effect flattened out above a range of two Barks. This frequency domain accords to critical band characteristics of the peripheral and central auditory system. The differences of early neuronal encoding of both formants relate to the predominant role of F2 for the encoding of stop consonants.

Adult↗

PubMed2002

Cerebellum and speech perception: a functional magnetic resonance imaging study.

A variety of data indicate that the cerebellum participates in perceptual tasks requiring the precise representation of temporal information. Access to the word form of a lexical item requires, among other functions, the processing of durational parameters of verbal utterances. Therefore, cerebellar dysfunctions must be expected to impair word recognition. In order to specify the topography of the assumed cerebellar speech perception mechanism, a functional magnetic resonance imaging study was performed using the German lexical items "Boden" ([bodn], Engl. "floor") and "Boten" ([botn], "messengers") as test materials. The contrast in sound structure of these two lexical items can be signaled either by the length of the wordmedial pause (closure time, CLT; an exclusively temporal measure) or by the aspiration noise of wordmedial "d" or "t" (voice onset time, VOT; an intrasegmental cue). A previous study found bilateral cerebellar disorders to compromise word recognition based on CLT whereas the encoding of VOT remained unimpaired. In the present study, two series of "Boden - Boten" utterances were resynthesized, systematically varying either in CLT or VOT. Subjects had to identify both words "Boden" and "Boten" by analysis of either the durational parameter CLT or the VOT aspiration segment. In a subtraction design, CLT categorization as compared to VOT identification (CLT - VOT) yielded a significant hemodynamic response of the right cerebellar hemisphere (neocerebellum Crus I) and the frontal lobe (anterior to Broca's area). The reversed contrast ( VOT - CLT) resulted in a single activation cluster located at the level of the supratemporal plane of the dominant hemisphere. These findings provide first evidence for a distinct contribution of the right cerebellar hemisphere to speech perception in terms of encoding of durational parameters of verbal utterances. Verbal working memory tasks, lexical response selection, and auditory imagery of word strings have been reported to elicit activation clusters of a similar location. Conceivably, representation of the temporal structure of speech sound sequences represents the common denominator of cerebellar participation in cognitive tasks acting on a phonetic code.

Acoustic Stimulation↗

PubMed2002

Mismatch responses to randomized gradient switching noise as reflected by fMRI and whole-head magnetoencephalography.

The central auditory system of the human brain uses a variety of mechanisms to analyze auditory scenes, among others, preattentive detection of sudden changes in the sound environment. Electroencephalography (EEG) and magnetoencephalography (MEG) provide a measure to monitor neuronal cortical currents. The mismatch negativity (MMN) or field (MMNm) reflect preattentive activation in response to deviants within a sequence of homogenous auditory stimuli. Functional magnetic resonance imaging (fMRI) allows for a higher spatial resolution as compared to the extracranial electrophysiological techniques. The image encoding gradients of echo planar imaging (EPI) sequences, however, elicit an interfering background noise. To circumvent this shortcoming, the present study applied multi-echo EPI mimicking an auditory oddball design. The gradient trains (SOA = 800 msec, 94.5 dB SPL, stimulus duration = 152 msec) comprised amplitude (-9 dB) and duration (76 msec) deviants in a randomized sequence. Moreover, the scanner noise was recorded and applied in a whole-head MEG device to validate the properties of this specific material. Robust fMRI activation patterns emerged in response to the deviant gradient switching. Changes in amplitude activated the entire auditory cortex, whereas the duration deviants elicited right-lateralized signal increase in secondary areas. The recorded scanner noise evoked reliably right-lateralized mismatch MEG responses. Source localization was in accordance with activation of secondary auditory cortex. The presented paradigm provides a robust and feasible tool to study the functional anatomy of early cognitive auditory processing in clinical populations such as schizophrenia.

Acoustic Stimulation↗

PubMed2002

Hemispheric lateralization effects of rhythm implementation during syllable repetitions: an fMRI study.

Rhythm in terms of the modulation of syllable durations represents an information-bearing feature of verbal utterances contributing both to the meaning of a sentence (linguistic prosody) as well as a speaker's emotional expression (affective prosody). In order to delineate the neural structures subserving rhythmic shaping of speech production, functional magnetic resonance imaging (fMRI) was performed during (a) isochronous syllable repetitions and (b) production of syllable triplets with lengthening either of the initial or final unit. A cognitive subtraction approach (rhythmic versus isochronous iterations) revealed activation of right-sided perisylvian areas (superior temporal gyrus, Broca analogue and adjacent premotor cortex) as well as contralateral subcortical structures (putamen and thalamus). Presumably, these responses reflect a right-hemisphere rehearsal mechanism of rhythmic patterns and left-hemisphere monitoring of verbal output.

Acoustic Stimulation↗

PubMed2002

Functional cerebral asymmetries of pitch processing during dichotic stimulus application: a whole-head magnetoencephalography study.

Dichotic listening (DL) studies indicate higher proficiency of the right cerebral hemisphere in processing the pitch of auditory events. Especially, acoustic stimuli of a rich harmonic structure such as square waves (complex tones) elicit a left ear advantage (LEA) under dichotic stimulus application. In order to investigate the timing of early sensory encoding at the level of the supratemporal plane, whole-head magnetoencephalography (MEG; 151 channels) recordings were performed in 20 right-handed subjects using an oddball paradigm based on dichotically applied complex tones. In contrast to electroencephalography (EEG) and event related potentials (ERP), this technique separately measures neuronal activity of left and right auditory cortex. Neuromagnetic responses were obtained both during preattentive stimulus processing, as well as during a pitch detection task. Rare stimuli presented to the left ear elicited a stronger magnetic analogue of mismatch negativity (MMNm) over both hemispheres and gave rise to shorter latencies of the contralateral mismatch fields than right ear deviants. In conclusion, the present data provide first evidence for functional laterality effects even at the level of preattentive pitch processing within the auditory cortex.

Acoustic Stimulation↗

PubMed2002

Hemispheric lateralization of the processing of consonant-vowel syllables (formant transitions): effects of stimulus characteristics and attentional demands on evoked magnetic fields.

It is still unsettled in how far temporal resolution of dynamic acoustic events (formant transitions) or phonetic/linguistic processes contribute to predominant left-hemisphere encoding of consonant-vowel syllables. To further elucidate the underlying mechanisms, evoked magnetic fields in response to consonant-vowel events (synthetic versus spoken) were recorded (oddball design: standards=binaural/ba/, deviants=dichotic/ba/-/da/; 20 right-handed subjects) under different attentional conditions (visual distraction versus stimulus identification). Spoken events yielded a left-lateralized peak phase of the mismatch field (MMF; 150-200ms post-stimulus onset) in response to right-ear deviants during distraction. By contrast, pre-attentive processing of synthetic items gave rise to a left-enhanced MMF onset (100ms), but failed to elicit later lateralization effects. In case of directed attention, synthetic deviants elicited a left-pronounced MMF peak resembling the pre-attentive response to natural syllables. These interactions of MMF asymmetry with signal structure and attentional load indicate two distinct successive left-lateralization effects: signal-related operations and representation of 'phonetic traces'. Furthermore, a right-lateralized early MMF component (100ms) emerged in response to natural syllables during pre-attentive processing and to synthetic stimuli in case of directed attention. Conceivably, these effects indicate right hemisphere operations prior to phonetic evaluation such as periodicity representation. Two distinct time windows showed correlations between dichotic listening performance and ear effects on magnetic responses reflecting early gain factors (ca. 75ms post-stimulus onset) and binaural fusion strategies (ca. 200ms), respectively. Finally, gender interacted with MMF lateralization, indicating different processing strategies in case of artificial speech signals.

Adult↗

PubMed2002

Speech perception deficits in Parkinson's disease: underestimation of time intervals compromises identification of durational phonetic contrasts.

Besides motor, vegetative, and cognitive signs, patients suffering from Parkinson's disease (PD) may show distinct perceptual deficits such as underestimation of time intervals extending across several seconds. Assuming this impairment also to affect the domain of tens of milliseconds, disrupted encoding of the acoustic speech signal with respect to segment durations conveying linguistic information must be expected. To test this hypothesis, 10 PD patients and matched controls performed an identification task using a series of 10 stimuli derived from the utterance "Boten" (/bo:tn/, 'messengers'; produced with nasal plosion) by exclusive manipulation of occlusion length (110-20 ms in steps of 10 ms). Under these conditions, word-medial silence cues the voicing category of the respective stop consonant. Seven PD subjects showed normal identification curves, i.e., categorized the shortest and longest stimuli with high probability each as the minimal pair cognates "Boden" and "Boten," respectively. In contrast, the remaining three patients labeled all items across the complete range of occlusion lengths as "Boden." A subsequent experiment found a horizontal shift of the identification curves toward larger signal durations (> 120 ms) in these three subjects. Bilateral cerebellar degeneration has been found to yield a different response pattern, i.e., near-chance level of performance. Considering recent information-processing models of scalar interval timing, striatal disorders seem to slow down an oscillatory pacemaker, whereas cerebellar dysfunctions may impair comparison of measured durations with stored reference memory traces.

Adult↗

PubMed2002

Reorganization of speech production at the motor cortex and cerebellum following capsular infarction: a follow-up functional magnetic resonance imaging study.

Based on clinical data, Geschwind assumed left hemisphere dominance of speech production to extend to the cortical representation of articulatory and phonatory functions at the motor cortex. This author suggested, furthermore, that the clinical observation of rapid recovery from articulatory impairments after damage to the left-sided corticobulbar tracts reflects compensatory activation of an alternative pathway involving the contralateral pre-central gyrus and its efferent projections. In order to test this hypothesis, functional magnetic resonance imaging (fMRI) was performed 4 and 35 days after stroke in a 38-year-old man who had experienced sudden speech deterioration ('dysarthric speech') concomitant with weakness of the right upper limb and the right side of the face. Computerized tomography demonstrated an ischaemic infarction within the left internal capsule. The patient fully recovered from dysarthria within 9 days. Activation of the right hemisphere analogues of Broca and Wernicke areas has been assumed to contribute to recovery from aphasia. As a further aspect of the reorganization of speech function, the present case study demonstrates for the first time by means of fMRI a selective 'shift' of the cortical representation of speech motor control to the right Rolandic cortex and the left cerebellum during restitution of articulation in a case of transient dysarthria following infarction of the left internal capsule.

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↗

PubMed1998

Emotional processing following cortical and subcortical brain damage: contribution of the fronto-striatal circuitry.

The present study examined the differential contribution of cortical and subcortical brain structures in emotional processing by comparing patients with focal cortical lesions (n = 32) to those with primarily subcortical dysregulation of the basal ganglia (Parkinson's disease n = 14). A standardized measure of emotional perception (Tübingen Affect Battery) was used. Only patients in the more advanced stages of Parkinson's disease and patients with focal damage to the (right) frontal lobe differed significantly from controls in both facial expression and affective prosody recognition. The findings imply involvement of the fronto-striatal circuitry in emotional processing.

Journal Article↗

PubMed1998

Role of the striatum and the cerebellum in motor skill acquisition.

Motor skill acquisition was investigated in patients with Parkinson's disease (PD) or cerebellar dysfunction using two sensory-guided tracking tasks. The subjects had to learn to track a visual target (a square) on a computer screen by moving a joystick under two different conditions. In the unreversed task, the horizontal target movements were semi-predictable and could be anticipated. In the reversed task, the horizontal movements of a pointer which had to be kept within the target square were mirror-reversed to the joystick movements. PD patients showed intact learning of the semi-predictable task and reduced learning of the mirror-reversed task; patients with cerebellar dysfunction showed the opposite pattern. These findings are discussed in relation to the differential contribution of the cerebellum and the striatum to motor skill acquisition: the cerebellum appears to participate in the implementation of anticipatory movements, whereas the striatum may be critically involved in types of motor learning which require a high degree of internal elaboration.

Journal Article↗