Biomedical subjects

H Scheich

Publications and source records attributed to H Scheich.

At least 19 recordsLinked to original sources

PubMed2006

Multisensory processing via early cortical stages: Connections of the primary auditory cortical field with other sensory systems.

It is still a popular view that primary sensory cortices are unimodal, but recent physiological studies have shown that under certain behavioral conditions primary sensory cortices can also be activated by multiple other modalities. Here, we investigate the anatomical substrate, which may underlie multisensory processes at the level of the primary auditory cortex (field AI), and which may, in turn, enable AI to influence other sensory systems. We approached this issue by means of the axonal transport of the sensitive bidirectional neuronal tracer fluorescein-labeled dextran which was injected into AI of Mongolian gerbils (Meriones unguiculatus). Of the total number of retrogradely labeled cell bodies (i.e. cells of origin of direct projections to AI) found in non-auditory sensory and multisensory brain areas, approximately 40% were in cortical areas and 60% in subcortical structures. Of the cell bodies in the cortical areas about 82% were located in multisensory cortex, viz., the dorsoposterior and ventroposterior, posterior parietal cortex, the claustrum, and the endopiriform nucleus, 10% were located in the primary somatosensory cortex (hindlimb and trunk region), and 8% in secondary visual cortex. The cortical regions with retrogradely labeled cells also contained anterogradely labeled axons and their terminations, i.e. they are also target areas of direct projections from AI. In addition, the primary olfactory cortex was identified as a target area of projections from AI. The laminar pattern of corticocortical connections suggests that AI receives primarily cortical feedback-type inputs and projects in a feedforward manner to its target areas. Of the labeled cell bodies in the subcortical structures, approximately 90% were located in multisensory thalamic, 4% in visual thalamic, and 6% in multisensory lower brainstem structures. At subcortical levels, we observed a similar correspondence of retrogradely labeled cells and anterogradely labeled axons and terminals in visual (posterior limitans thalamic nucleus) and multisensory thalamic nuclei (dorsal and medial division of the medial geniculate body, suprageniculate nucleus, posterior thalamic cell group, zona incerta), and in the multisensory nucleus of the brachium of the inferior colliculus. Retrograde, but not anterograde, labeling was found in the multisensory pontine reticular formation, particularly in the reticulotegmental nucleus of the pons. Conversely, anterograde, but no retrograde, labeling was found in the visual laterodorsal and lateroposterior thalamic nuclei, in the multisensory peripeduncular, posterior intralaminar, and reticular thalamic nuclei, as well as in the multisensory superior and pericentral inferior colliculi (including cuneiform and sagulum nucleus), pontine nuclei, and periaqueductal gray. Our study supports the notion that AI is not merely involved in the analysis of auditory stimulus properties but also in processing of other sensory and multisensory information. Since AI is directly connected to other primary sensory cortices (viz. the somatosensory and olfactory ones) multisensory information is probably also processed in these cortices. This suggests more generally, that primary sensory cortices may not be unimodal.

Afferent Pathways↗

PubMed2004

Learning a new behavioral strategy in the shuttle-box increases prefrontal dopamine.

Using microdialysis from medial prefrontal cortex of gerbils during aversive auditory conditioning in the shuttle-box we have previously shown a transient increase of dopamine efflux correlated with the establishment of avoidance behavior. We hypothesized that the acquisition of a new behavioral strategy is generally accompanied by this extra prefrontal dopamine release. The present experiment aimed at further testing this hypothesis. In a pre-training period in the shuttle-box the gerbils acquired an active avoidance response by generalizing two different tone signals to a GO-meaning (change of shuttle-box compartment). Thereafter, they were subjected in relearning sessions to differentially associate the known tone stimuli with GO- and NOGO- (no change of shuttle-box compartment) conditions, respectively. The following formation of discrimination behavior led to a similar extra dopamine increase as found during establishment of the avoidance strategy. This significant enhancement was limited to rapidly relearning individuals. Furthermore, the dopamine increase attenuated in these animals with increasing performance during the course of the discrimination training, similar to the retrieval stage of the avoidance strategy. Therefore, the dopamine system seems to be critically involved in the initial formation of associations for new behavioral strategies, i.e. learning. We assume that the prefrontal dopamine increase during initial learning of the complex discrimination behavior indicates an involvement of working memory principles and a goal-directed formation of a behavioral strategy.

Animals↗

PubMed2003

Form-from-motion: MEG evidence for time course and processing sequence.

The neural mechanisms and role of attention in the processing of visual form defined by luminance or motion cues were studied using magnetoencephalography. Subjects viewed bilateral stimuli composed of moving random dots and were instructed to covertly attend to either left or right hemifield stimuli in order to detect designated target stimuli that required a response. To generate form-from-motion (FFMo) stimuli, a subset of the dots could begin to move coherently to create the appearance of a simple form (e.g., square). In other blocks, to generate form-from-luminance (FFLu) stimuli that served as a control, a gray stimulus was presented superimposed on the randomly moving dots. Neuromagnetic responses were observed to both the FFLu and FFMo stimuli and localized to multiple visual cortical stages of analysis. Early activity in low-level visual cortical areas (striate/early extrastriate) did not differ for FFLu versus FFMo stimuli, nor as a function of spatial attention. Longer latency responses elicited by the FFLu stimuli were localized to the ventral-lateral occipital cortex (LO) and the inferior temporal cortex (IT). The FFMo stimuli also generated activity in the LO and IT, but only after first eliciting activity in the lateral occipital cortical region corresponding to MT/V5, resulting in a 50-60 msec delay in activity. All of these late responses (MT/V5, LO, and IT) were significantly modulated by spatial attention, being greatly attenuated for ignored FFLu and FFMo stimuli. These findings argue that processing of form in IT that is defined by motion requires a serial processing of information, first in the motion analysis pathway from V1 to MT/V5 and thereafter via the form analysis stream in the ventral visual pathway to IT.

Attention↗

PubMed2003

Early and late patterns of stimulus-related activity in auditory cortex of trained animals.

Epidural electrocorticograms over the right auditory cortex (field AI) were measured using implanted 18-channel (3 x 6) electrode arrays in four animals (Mongolian gerbil) trained to discriminate between a rising and a falling frequency modulated tone (frequency range 2-4 kHz). Using a previously introduced classification procedure, transient patterns of cortical activity suitable to discriminate between the rising and the falling modulation were identified. Early (locked to stimulus onset) and late (emerging at variable times poststimulus) patterns could be differentiated. Deletion of increasing numbers of randomly selected electrodes was used to determine a critical density of recording channels required to capture the discriminative power of the early and late patterns. Statistical analysis of the classification revealed a sigmoid dependence of the discriminative power from the number of remaining electrodes with an inflection point at 12 electrodes. The analysis of the minima of the classification statistic revealed that in the early patterns discriminative information was focal on regions corresponding to the tonotopic representation of the stimuli, whereas in late patterns this information seemed to be distributed nonfocally across larger cortical regions. This analysis supports the previous notion of the coexistence of topographically organized activity states related to the physical stimulus features and nontopographically organized states determined largely by intrinsic factors (Ohl et al. 2001).

Acoustic Stimulation↗

PubMed2003

Analysis of evoked and emergent patterns of stimulus-related auditory cortical activity.

Cortical activity contains both evoked patterns and emergent patterns of stimulus-related activity. Here we compared evoked and emergent patterns in the primary auditory cortex, field AI, of the gerbil by studying the differential effects of diluting spatial information about the patterns on their geometric dissimilarity by randomly removing channels from the recording data. This identified the sets of most relevant channels for the discrimination of stimuli in both types of patterns. In the evoked patterns the sets of most discriminative channels were found to be focally organized at locations corresponding to the thalamically relayed input into the cortical tonotopic map. In the emergent patterns the sets of most discriminative channels were broadly distributed and held no apparent relationship to the tonotopic map. The results indicate the coexistence in the same neuronal tissue of a topographic mapping principle for the evoked activity and a holographic mapping principle for the emergent activity.

Acoustic Stimulation↗

PubMed2002

Phonetic perception and the temporal cortex.

Recent functional neuroimaging studies have emphasized the role of the different areas within the left superior temporal sulcus (STS) for the perception of various speech stimuli. We report here the results of three independent studies additionally demonstrating hemodynamic responses in the vicinity of the planum temporale (PT). In these studies we used consonant-vowel (CV) syllables, tones, white noise, and vowels as acoustic stimuli in the context of whole-head functional magnetic resonance imaging, applying a long TR to attenuate possible masking effects by the scanner noise. To summarize, we obtained the following results for the contrasts comparing hemodynamic responses obtained during the perception of CV syllables compared to tones or white noise: (i) stronger activation in the vicinity of the left PT with two distinct foci of activation, one in a lateral position and the other more medial in the vicinity of Heschl's sulcus; (ii) stronger activation in the vicinity of the right PT; and (iii) stronger bilateral activation within the mid-STS. Further contrasts revealed the following findings: (iv) stronger bilateral activation to CV syllables than to vowels in the medial PT, (v) stronger left-sided activation to CV syllables than to vowels in the mid-STS, and (vi) stronger activation to CV syllables with voiceless initial consonants than to CV syllables with voiced initial consonants in the left medial PT. The results are compatible with the hypothesis that the STS contains neurons specialized for speech perception. However, these results also emphasize the role of the PT in the analysis of phonetic features, namely the voice-onset-time. Yet this does not mean that the PT is solely specialized for phonetic analysis. We hypothesize rather that the PT contains neurons specialized for the analysis of rapidly changing cues as was suggested by P. Tallal et al. (1993, Ann. N. Y. Acad. Sci. 682: 27-47).

Acoustic Stimulation↗

PubMed2001

Optical imaging of neural activity in multiple auditory cortical fields of guinea pigs.

Neural activity of multiple fields in the auditory cortex of anesthetized guinea pigs in response to pure tones was visualized by optical recording using a voltage-sensitive dye (RH795). Ten auditory fields were identified based on the tonotopic organization and response latency: the core fields consisting of the primary (AI) and secondary (AII) fields and surrounding belt areas consisting of dorso-anterior (DA), dorsal (D), dorso-posterior (DP), posterior (P), ventro-posterior (VP), ventro-medial (VM), ventro-anterior (VA) and ventral (V) fields. Tonotopic organization was observed in all the fields apart from DA, D, DP and V. Spatio-temporal displays suggest that the auditory information spreads from the core fields of AI and AII to belt fields via three distinct (dorsocaudal, caudal and ventrorostral) pathways.

Acoustic Stimulation↗

PubMed2001

Change in pattern of ongoing cortical activity with auditory category learning.

Humans are able to classify novel items correctly by category; some other animals have also been shown to do this. During category learning, humans group perceptual stimuli by abstracting qualities from similarity relationships of their physical properties. Forming categories is fundamental to cognition and can be independent of a 'memory store' of information about the items or a prototype. The neurophysiological mechanisms underlying the formation of categories are unknown. Using an animal model of category learning, in which frequency-modulated tones are distinguished into the categories of 'rising' and 'falling' modulation, we demonstrate here that the sorting of stimuli into these categories emerges as a sudden change in an animal's learning strategy. Electro-corticographical recording from the auditory cortex shows that the transition is accompanied by a change in the dynamics of cortical stimulus representation. We suggest that this dynamic change represents a mechanism underlying the recognition of the abstract quality (or qualities) that defines the categories.

Animals↗

PubMed2001

Comparative electrophysiological and hemodynamic measures of neural activation during memory-retrieval.

The spatial and temporal characteristics of the brain processes underlying memory retrieval were studied with both event-related potentials (ERP) and positron emission tomography (PET) techniques. Subjects studied lists of 20 words and then performed episodic (old/new judgment) or semantic (living/nonliving decision) retrieval tasks on multiple four-item test lists, each lasting 10 sec. The PET and ERP measurements at test were assessed in relation to both the task (episodic vs. semantic) and the item (old vs. new or living vs. nonliving). Episodic retrieval was associated with increased blood flow in the right frontal lobe (Brodmann Area 10) and a sustained, slowly developing positive ERP shift recorded from the right frontopolar scalp. Semantic retrieval was associated with increased blood flow in the left frontal (Area 45) and temporal (Area 21) lobes but no clear ERP concomitant. The two retrieval tasks also differed from each other in the ERPs to single items in an early (300-500 ms) time window. Item-related comparisons yielded convergent results mainly if the retrieved information was relevant to the given task (e.g., old/new items during episodic retrieval and living/nonliving items during semantic retrieval). Episodically retrieved old items were associated with increased blood flow in the left medial temporal lobe and a transient increase in the amplitude of the late positive component (500-700 ms) of the ERP. Semantically retrieved living items were associated with increased blood flow in the left frontal cortex and anterior cingulate and a transient late frontal slow wave (700-1,500 ms) in the ERPs. These results indicate that the brain regions engaged in memory retrieval are active in either a sustained or transient manner. They map task-related processes to sustained and item-related processes to transient neural activity. But they also suggest that task-related factors can transiently affect early stages of item processing.

Adult↗

PubMed2001

Activation of the dopaminergic system of medial prefrontal cortex of gerbils during formation of relevant associations for the avoidance strategy in the shuttle-box.

1. A detailed analysis of behavior is a prerequisite for identification of components of information processing during learning. 2. Components of shuttle-box learning like the signal detection and signal evaluation can be differentiated using behavioral events such as the attention response and the orienting response. 3. Chiefly during evaluation of signal meaning in the acquisition phase of the avoidance strategy the extracellular DA is increased in mPFC. 4. The kinetics of prefrontal dopaminergic activation from trial to trial depends on the stage of avoidance learning. 5. The increase of DA in mPFC can be an indicator for the involvement of working memory principles in signal evaluation stages of conditioning.

Animals↗

PubMed2001

Auditory perception of laughing and crying activates human amygdala regardless of attentional state.

Adequate behavioral responses to socially relevant stimuli are often impaired after lesions of the amygdala. Such lesions concern especially the recognition of facial and sometimes of vocal expression of emotions. Using low-noise functional magnetic resonance imaging (fMRI), we investigated in which way the amygdala, auditory cortex and insula are involved in the processing of affective nonverbal vocalizations (Laughing and Crying) in healthy humans. The same samples of male and female Laughing and Crying were presented in different experimental conditions: Simply listening to the stimuli, self-induction of the corresponding emotions while listening, and detection of artificial pitch shifts in the same stimuli. All conditions activated the amygdala similarly and bilaterally, whereby the amount of activation was larger in the right amygdala. The auditory cortex was more strongly activated by Laughing than by Crying with a slight right-hemisphere advantage for Laughing, both likely due to acoustic stimulus features. The insula was bilaterally activated in all conditions. The mean signal intensity change with stimulation was much larger in the amygdala than in auditory cortex and insula. The amygdala results seem to be in accordance with the right-hemisphere hypothesis of emotion processing which may not be applicable as strongly to the level of auditory cortex or insula.

Acoustic Stimulation↗

PubMed2001

Short-term functional plasticity in the human auditory cortex: an fMRI study.

Applying functional magnetic resonance imaging (fMRI) techniques, hemodynamic responses elicited by sequences of pure tones of 950 Hz (standard) and deviant tones of 952, 954, and 958 Hz were measured before and 1 week after subjects had been trained at frequency discrimination for five sessions (over 1 week) using an oddball procedure. The task of the subject was to detect deviants differing from the standard stimulus. Frequency discrimination improved during the training session for three subjects (performance gain: T+) but not for three other subjects (no performance gain: T-). Hemodynamic responses in the auditory cortex comprising the planum temporale, planum polare and sulcus temporalis superior significantly decreased during training only for the T+ group. These activation changes were strongest for those stimuli accompanied by the strongest performance gain (958 and 954 Hz). There was no difference with respect to the hemodynamic responses in the auditory cortex for the T- group and the control group (CO) who did not received any pitch discrimination training. The results suggest a plastic reorganization of the cortical representation for the trained frequencies which can be best explained on the basis of 'fast learning' theories.

Acoustic Stimulation↗

PubMed2001

A semiautomatic method for adding behavioral data to videotape records in combination with the Noldus Observer system.

The Observer 3.0 (Noldus, 1991) was used as the base for a time-saving fine analysis of animal behavior. A PC controlled a shuttlebox and a shuttlebox control unit. Learning behavior was recorded on videotapes by an S-VHS camcorder with vertical interval time code (VITC), which was used to generate an observational data file (ODF). The observational system was enhanced by automatically recorded status signals from the PC as event markers on the soundtrack of the videotape. These signals were used to subdivide a training session into numbered trials during generation of the ODF. They were later used for a PC-aided fine analysis of behavioral events, such as attention responses (AR) and orienting responses (OR) during shuttlebox learning. In this way, a large number of both automatically inserted PC event markers and manually inserted, key-defined behavioral events were registered and analyzed effectively in a semiautomatic fashion. The system is illustrated with an analysis of shuttle-box avoidance data from gerbils (Meriones unguiculatus).

Acoustic Stimulation↗

PubMed2000

Stages of avoidance strategy formation in gerbils are correlated with dopaminergic transmission activity.

This detailed analysis of behavior is aimed at the differentiation of the components of information processing during associative conditioning. In gerbils, the influences of various acquired non-avoidance strategies as pre-experience were studied during the learning of a standard avoidance task in the same shuttle-box. Identical cue stimuli, frequency-modulated tones as conditioned stimuli and electric footshocks as unconditioned stimuli, were used in various behavioral tasks. In addition to common parameters such as avoidance performance and reaction times, behavioral events such as the attention response and the orienting response were quantified. Thereby, components of shuttle-box learning such as signal detection and signal evaluation were found to be affected by pre-experience-dependent dynamics. Using a microdialysis technique during avoidance learning in the shuttle-box, we found that only strategy formation was correlated with high dopamine levels in medial prefrontal cortex. The increase in dopamine in medial prefrontal cortex may be an indicator of the involvement of working memory principles in signal evaluation stages of conditioning.

Animals↗

PubMed2000

New insights into the hemodynamic blood oxygenation level-dependent response through combination of functional magnetic resonance imaging and optical recording in gerbil barrel cortex.

Fast, low-angle shoot functional magnetic resonance imaging (fMRI), based on the blood oxygenation level-dependent (BOLD) effect, was combined with optical recording of intrinsic signals (ORIS) and 2-deoxyglucose labeling in gerbil barrel cortex. We observed over the activated barrel a positive BOLD signal and increased levels of deoxyhemoglobin and total hemoglobin during each period of prolonged (30 sec) D2 vibrissal stimulation. These data show that the hemodynamic basis of this fMRI signal is not necessarily a washout of deoxyhemoglobin, as generally assumed. Instead, they suggest that a positive BOLD signal can also be caused by a local increase of blood volume, even if deoxyhemoglobin levels are persistently elevated. We also show that this alternative interpretation is consistent with theoretical models of the BOLD signal. The changes in BOLD signal and blood volume, which are most tightly correlated with the periodic stimulation, peak at the site of neuronal activation. These results contribute to the understanding of the hemodynamic mechanisms underlying the BOLD signal and also suggest analysis methods, which improve the spatial localization of neuronal activation with both fMRI and ORIS.

Animals↗

PubMed2000

The inhibitory influence of an acquired escape strategy on subsequent avoidance learning in gerbils.

In gerbils an acquired non-avoidance strategy as pre-experience in a shuttle-box was studied in its influence on the learning of a standard avoidance paradigm. Thereby the same cue stimuli, frequency modulated tones (CS) and electric footshocks (US) were used in different behavioral paradigms. In the preexperience sessions the interstimulus interval between CS and US and on the other hand the escapability or inescapability of the US was varied. It was found that the experience with a relatively long interstimulus interval led to a prolonged maintenance of an acquired escape strategy during subsequent standard avoidance learning. This effect increased with the preexperience of an inescapable US. Additional insights into the temporal inhibition of avoidance learning by the pre-experience were provided by behavioral events like attention responses and orienting responses reflecting components of information processing.

Acoustic Stimulation↗

PubMed2000

An interspike interval method for computing phase locking from neural firing.

Inner hair cells (IHCs) transform the mechanical movements of the basilar membrane into electrical impulses. The impulse coding of the IHCs is the main information carrier in the auditory process and is the basis for improvements of cochlea implants as well as for low rate, high-quality speech processing and compression. This paper shows how to compute the speech signal from the neural firing based on the analysis of the interspike interval histogram. This new approach solves problems that other standard analysis methods do not solve sufficiently well.

Action Potentials↗

PubMed2000

Early unilateral auditory deprivation increases 2-deoxyglucose uptake in contralateral auditory cortex of juvenile Mongolian gerbils.

The effects of early onset, unilateral conductive hearing loss on tone-induced 2-deoxyglucose (2-DG) uptake in the auditory cortex of juvenile Mongolian gerbils (Meriones unguiculatus) were studied. Atresia of the left ear canal was induced at postnatal day 9 (P9) to achieve reversible auditory deprivation prior to onset of hearing (around P12). Atresia either persisted (ATR, n=4) or the canal was opened 15 min before the 2-DG experiments (RE, n=4) at P27. Control animals were either non-deprived (CON, n=4), or their left ears were plugged acutely (PAX, n=4). In PAX, 2-DG uptake in primary auditory cortex (AI) and anterior auditory field (AAF) was lower in right than in left AI and AAF. In contrast, in ATR and RE, uptake was significantly higher on the right side contralateral to the atresia. Hence, atresia during early development leads to plastic changes resulting in an interhemispheric imbalance of functional metabolism in favor of the auditory cortex contralateral to the manipulated ear. Distances between tone-induced 2-DG labeling in AI and AAF were increased in PAX, but smaller in ATR in the right compared to the left hemisphere, suggesting effects of atresia also on spatial relations in cortical tonotopic maps.

Acoustic Stimulation↗