Search PubMed⌕ Search

Biomedical subjects

H J Heinze

Publications and source records attributed to H J Heinze.

At least 19 recordsLinked to original sources
PubMed2000

A magnetoencephalographic study of brain activity related to recognition memory in healthy young human subjects.

Neural activity associated with recognition memory was investigated using magnetencephalography (MEG) in healthy young subjects. At sensor sites overlying frontal and temporoparietal cortices, magnetic evoked fields (MEFs) revealed a difference between studied and unstudied stimuli, which onset about 400 ms following stimulus onset and lasted about 600 ms. MEG yielded reliable source information revealing the activity of three independent dipoles, located in the right medial temporal lobe (MTL), the right inferior frontal and the left inferior parietal cortices. Our findings suggest that neural activity underlying recognition memory from both superficial and deep brain structures can be monitored by MEG.

Adult↗
PubMed2000

An electrophysiological study of the insertion of overt response choice.

Using electrophysiological measures, the authors studied changes in prestimulus state, stimulus identification, and response-related processing when, in a go/no-go task, forced choice between 2 overt go responses was inserted. The authors observed decreased prestimulus motor preparation (electromyogram), no change in stimulus identification time (selection negativity), a minor increase in response selection time (lateralized readiness potential), a large increase in response preparation time (lateralized readiness potential), a minor effect on response execution time (electromyogram), and a decrease in the activation of a response-inhibition process on no-go trials (frontal event-related potential). The existence of the response-inhibition process was verified by the presence of inverted lateralized readiness potentials on no-go trials. Pure insertion of response choice in a task seems impossible because the choice between activation and inhibition (go/no-go) always seems already present.

Adolescent↗
PubMed2000

Amantadine influences cognitive processing in patients with multiple sclerosis.

We investigated the effect of amantadine on cognitive processing in patients with multiple sclerosis (MS) and fatigue with objective electrophysiological measures. Behavioral methods (Reaction Time, RT) and two different Event Related Potential (ERP) components measuring i) stimulus selection (Selection Negativity, SN) and ii) response selection (Lateralized Readiness Potential, LRP) were employed. Twenty-four patients with clinical definite MS (10 relapsing remitting and 14 secondary progressive) and confirmed fatigue in the past three months (Fatigue Severity Scale (FSS) > 4) were included. Patients were randomized in a double-blind, placebo-controlled cross-over design. We found a difference between the two treatments for ERP measures to stimuli with relevant colour starting at about 200 ms. This negativity had a higher amplitude during amantadine treatment regardless of treatment order. The RT did not differ significantly between the treated and untreated groups. Additional analysis indicated that patients with a disease duration of less than 7 years had a significant test position (practice effect), but no treatment effect, while patients with a longer MS duration showed no practice effect, but rather an improved reaction speed and increased ERP amplitude effects when treated with amantadine. The present findings suggest that amantadine exerts beneficial effects on early cognitive processes in patients with MS, but appears to be limited to subjects with a longer duration of the disease.

Adult↗
PubMed2000

Mitochondrial DNA abnormalities in skeletal muscle of patients with sporadic amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis is a neurodegenerative disease affecting the anterior horn cells of the spinal cord and cortical motor neurons. Previous findings have suggested a specific impairment of mitochondrial function in skeletal muscle of at least a limited number of patients. Applying flavoprotein/NAD(P)H autofluorescence imaging of mitochondrial function in saponin-permeabilized muscle fibres, we detected a heterogeneous distribution of the respiratory chain defect among individual fibres in muscle biopsies of patients (11 out of 17) with sporadic amyotrophic lateral sclerosis (SALS). These findings correlate with the presence of cytochrome c oxidase (COX)-negative muscle fibres detected histologically. We established the molecular basis for the decreased activities of NADH:CoQ oxidoreductase and COX in SALS muscle. In the skeletal muscle of the investigated patients, diminished levels (13 out of 17) or multiple deletions (one out of 17) of mitochondrial DNA (mtDNA) were observed. These alterations of mtDNA seem to be related to decreased levels of membrane-associated mitochondrial Mn-superoxide dismutase. Our results support the viewpoint that an oxygen radical-induced impairment of mtDNA is of pathophysiological significance in the aetiology of at least a subgroup of patients with SALS.

Adult↗
PubMed2000

Functional dissociation between medial and lateral prefrontal cortical spatiotemporal activation in negative and positive emotions: a combined fMRI/MEG study.

The orbitofrontal cortex has been cytoarchitectonically and connectionally subdivided into a medial and a lateral part which are assumed to subserve distinct functions in emotional processing. However the exact spatiotemporal mechanisms of negative and positive emotional processing in medial and lateral orbitofrontal cortex remain unclear. We therefore investigated spatiotemporal orbitofrontal and prefrontal cortical activation patterns during emotional stimulation in a combined fMRI/MEG study. We investigated 10 healthy subjects, 5 women and 5 men. Positive and negative pictures from the International Affective Picture system (IAPS) were used for emotional stimulation, whereas neutral and gray pictures were taken as control conditions. fMRI/MEG measurements covered the whole frontal lobe and a time window between -2000 and +200 ms around motor responses (right index finger extension) associated with each picture. Positively and negatively correlated activities were determined in various prefrontal/frontal cortical regions in fMRI. Isocontour maps and single dipoles in MEG were analyzed in 50 ms time windows ranging from -2000 to +200 ms. Dipoles and fMR images were mapped on three-dimensional anatomical MRI so that anatomical localization of single dipoles and regional fMRI activity could be compared. Both negative and positive emotional conditions differed from non-emotional control conditions by strong orbitofrontal and lateral prefrontal activation as well as by the presence of early magnetic fields (-1700 to +1100 ms). Negative emotional processing was characterized by strong medial orbitofrontal activation and earlier (-1700 ms), stronger and more medially oriented orbitofrontal dipoles. In contrast positive emotional processing showed a rather strong activation in lateral prefrontal cortex with later (-1500 ms), weaker and more laterally oriented orbito and prefrontal dipoles. Negative emotional processing can be characterized by strong and early medial orbitofrontal cortical activation, whereas positive emotional processing showed rather later and weaker activation in lateral orbitofrontal/prefrontal cortex. Such a functional dissociation between medial and lateral orbito-frontal/prefrontal cortex during negative and positive emotional processing lends further support to the assumption of a functional subdivision in the orbitofrontal cortex.

Adult↗
PubMed2000

Impairment and recovery of elementary cognitive function induced by hypoglycemia in type-1 diabetic patients and healthy controls.

Although neuroendocrine changes after induction of hypoglycemia, in patients with diabetes and healthy persons, are thoroughly investigated, cognitive adaptation processes are still insufficiently understood. Changes in cognitive functions are mainly investigated by psychometric tests, which represent a summation of different cognitive processes. We aimed at dissecting cognitive adaptation into single components, i.e. stimulus selection, response choice, and reaction speed during a hyperinsulinemic hypoglycemic clamp in patients with type-1 diabetes and matched healthy controls. Using novel neurophysiological analyses, the event-related potentials of early stimulus selection (selection negativity) and response selection (lateralized readiness potential) were studied, in addition to reaction time (RT). A total of 12 diabetic patients and 12 normal volunteers were studied while receiving a hyperinsulinemic hypoglycemic clamp. RTs and the event-related potentials related to stimulus selection and response selection were significantly delayed during hypoglycemia in both groups, whereas early evoked potentials (P100) were unaltered. This suggests that hypoglycemia delays stimulus selection, with the consequence that also central and motor processing are delayed. In addition, patients with diabetes showed an earlier negative shift over the frontal cortex, which, when compared with the controls, reveals better adaptation to hypoglycemia in frontal cortical brain regions. After restoration of euglycemia stimulus selection, response selection and RT returned to baseline level in the type-1 group. In the control group, however, response selection and RTs were still delayed. This suggests that type-1 patients, possibly because of the past occurrence of hypoglycemic events, might be able to better cope with the hypoglycemic state than healthy volunteers who lack such a history. In summary, our data demonstrate, for the first time, that cognitive adaptation processes to an experimental hypoglycemic episode can clearly be dissected into their single components.

Adrenocorticotropic Hormone↗
PubMed1999

Evidence relating human verbal memory to hippocampal N-methyl-D-aspartate receptors.

Studies in rodents and nonhuman primates have linked the activity of N-methyl-D-aspartate (NMDA) receptors within the hippocampus to animals' performance on memory-related tasks. However, whether these receptors are similarly essential for human memory is still an open question. Here we present evidence suggesting that hippocampal NMDA receptors, most likely within the CA1 region, do participate in human verbal memory processes. Words elicit a negative event-related potential (ERP) peaking around 400 ms within the anterior mesial temporal lobe (AMTL-N400). Ketamine, an NMDA-receptor antagonist, reduces the amplitude of the AMTL-N400 (in contrast to other hippocampal potentials) on initial presentation, eliminates the typical AMTL-N400 amplitude reduction with repetition, and leads to significant memory impairment. Of the various hippocampal subfields, only the density of CA1 neurons correlates with the word-related ERPs that are reduced by ketamine. Altogether, our behavioral, anatomical, and electrophysiological results indicate that hippocampal NMDA receptors are involved in human memory.

Adult↗
PubMed1999

An event-related brain potential correlate of visual short-term memory.

Event-related potentials (ERPs) were recorded as 12 subjects performed a delayed matching to sample task. We presented two bilateral abstract shapes and cued spatially which had to be memorized for a subsequent matching task: left, right or both. During memorization a posterior slow negative ERP wave developed over the hemisphere contralateral to the memorized shape. This effect was similar in high and low memory load trials while the memory figures were visible (for 1000 ms). As the figures disappeared (for 1500 ms), the effect persisted only in the low memory load conditions. We suggest that the contralateral negativity reflects a visual short-term memory process and that capacity limitation in the high memory load condition causes this process to collapse.

Adult↗
PubMed1999

Representations in human visual short-term memory: an event-related brain potential study.

Behavioral measures and event-related potentials (ERPs) were recorded from 12 subjects while performing three delayed matching-to-sample tasks. The task instructions indicated whether stimulus locations, shapes or conjunctions of locations and shapes had to be memorized and matched against a probe. Memory load was varied trial-by-trial by cueing one or two of three stimuli for memorization, followed by one probe. ERPs during memorization and probe response times varied as a function of memory load (posterior negative and anterior positive ERP wave), but not between single-feature and conjunction of features, nor was an interaction found between them. The results support and extend hypotheses by Luck and Vogel (Luck, S.J. and Vogel, E.K., The capacity of visual working memory for features and conjunctions. Nature, 390 (1997) 279-281.) that visual short-term memory stores conjunctions of features rather than single features.

Adult↗
PubMed1999

Neural correlates of recognition memory with and without recollection in patients with Alzheimer's disease and healthy controls.

To dissociate recognition memory with and without recollection, event-related potentials (ERPs) of patients with Alzheimer's disease (AD) and matched controls were recorded in a test of verbal recognition memory accompanied by a source judgement. AD patients who had smaller hippocampi showed a disability to recollect the study context (source). Their ERPs elicited by correctly recognized old words compared to new items were more positive only between 300 and 500 ms with a maximum over the frontal scalp. Controls exhibited a sustained old/new effect over left temporoparietal and frontal sites. The present findings suggest that preserved recognition memory in patients with mild AD is independent of hippocampally mediated processes recollecting episodic memories.

Aged↗
PubMed1999

Task-related and item-related brain processes of memory retrieval.

In all cognitive tasks, general task-related processes operate throughout a given task on all items, whereas specific item-related processes operate differentially on individual items. In typical functional neuroimaging experiments, these two sets of processes have usually been confounded. Herein we report a combined positron emission tomography and event-related potential (ERP) experiment that was designed to distinguish between neural correlates of task-related and item-related processes of memory retrieval. Two retrieval tasks, episodic and semantic, were crossed with episodic (old/new) and semantic (living/nonliving) properties of individual items to yield evidence of regional brain activity associated with task-related processes, item-related processes, and their interaction. The results showed that episodic retrieval task was associated with increased blood flow in right prefrontal and posterior cingulate cortex, as well as with a sustained right-frontopolar-positive ERP, but that the semantic retrieval task was associated with left frontal and temporal lobe activity. Retrieval of old items was associated with increased blood flow in the left medial temporal lobe and with a brief late positive ERP component. The results provide converging hemodynamic and electrophysiological evidence for the distinction of task- and item-related processes, show that they map onto spatially and temporally distinct patterns of brain activity, and clarify the hemispheric encoding/retrieval asymmetry (HERA) model of prefrontal encoding and retrieval asymmetry.

Adult↗
PubMed1999

An event-related brain potential study of visual selective attention to conjunctions of color and shape.

What cognitive processes underlie event-related brain potential (ERP) effects related to visual multidimensional selective attention and how are these processes organized? We recorded ERPs when participants attended to one conjunction of color, global shape and local shape and ignored other conjunctions of these attributes in three discriminability conditions. Attending to color and shape produced three ERP effects: frontal selection positivity (FSP), central negativity (N2b), and posterior selection negativity (SN). The results suggested that the processes underlying SN and N2b perform independent within-dimension selections, whereas the process underlying the FSP performs hierarchical between-dimension selections. At posterior electrodes, manipulation of discriminability changed the ERPs to the relevant but not to the irrelevant stimuli, suggesting that the SN does not concern the selection process itself but rather a cognitive process initiated after selection is finished. Other findings suggested that selection of multiple visual attributes occurs in parallel.

Adult↗
PubMed1999

Involvement of striate and extrastriate visual cortical areas in spatial attention.

We investigated the cortical mechanisms of visual-spatial attention while subjects discriminated patterned targets within distractor arrays. Functional magnetic resonance imaging (fMRI) was used to map the boundaries of retinotopic visual areas and to localize attention-related changes in neural activity within several of those areas, including primary visual (striate) cortex. Event-related potentials (ERPs) and modeling of their neural sources, however, indicated that the initial sensory input to striate cortex at 50-55 milliseconds after the stimulus was not modulated by attention. The earliest facilitation of attended signals was observed in extrastriate visual areas, at 70-75 milliseconds. We hypothesize that the striate cortex modulation found with fMRI may represent a delayed, re-entrant feedback from higher visual areas or a sustained biasing of striate cortical neurons during attention. ERP recordings provide critical temporal information for analyzing the functional neuroanatomy of visual attention.

Adult↗
PubMed1998

Verbal novelty detection within the human hippocampus proper.

Animal studies and neuropsychological tests of patients with temporal lobe epilepsy have demonstrated the importance of human medial temporal lobes for memory formation. In addition, more recent studies have shown that the human hippocampal region is also involved in novelty detection. However, the exact contribution of the hippocampus proper to these processes is still unknown. To examine further its role we compared event-related potentials recorded within the medial temporal lobes in 29 temporal lobe epilepsy patients with and 21 without hippocampal sclerosis. While in patients with extrahippocampal lesions but without hippocampal sclerosis event-related potentials to first presentations and repetitions of words were reduced on the side of the epileptogenic focus, in patients with hippocampal sclerosis only those to first presentations but not to repetitions were affected. Because sclerosis of the hippocampus proper selectively reduced event-related potentials to new but not old verbal stimuli, it can be concluded that the human hippocampus proper contributes to verbal novelty detection.

Adolescent↗
PubMed1998

Successful verbal encoding into episodic memory engages the posterior hippocampus: a parametrically analyzed functional magnetic resonance imaging study.

The medial temporal lobe (MTL) is essential for episodic memory encoding, as evidenced by memory deficits in patients with MTL damage. However, previous functional neuroimaging studies have either failed to show MTL activation during encoding or they did not differentiate between two MTL related processes: novelty assessment and episodic memory encoding. Furthermore, there is evidence that the MTL can be subdivided into subcomponents serving different memory processes, but the extent of this functional subdivision remains unknown. The aim of the present functional magnetic resonance imaging (fMRI) study was to investigate the role of the MTL in episodic encoding and to determine whether this function might be restricted to anatomical subdivisions of the MTL. Thirteen healthy volunteers performed a word list learning paradigm with free recall after distraction. Functional images acquired during encoding were analyzed separately for each participant by a voxel-wise correlation (Kendall's tau) between the time series of the T2*-signal intensity and the number of subsequently recalled words encoded during each particular scan. Of the 13 participants, 11 showed voxel clusters with statistically significant, positive correlations in the posterior part of the hippocampus. Across participants, an ANOVA on the number of voxels with significant, positive correlations within individually defined volumes of interest confirmed a statistically significant difference in activation for anterior versus posterior regions of the hippocampus. However, no differences between left and right hippocampal activation were revealed. Thus, these findings demonstrate that successful encoding into episodic memory engages neural circuits in the posterior part of the hippocampus.

Adolescent↗
PubMed1998

Brain potentials and syntactic violations revisited: no evidence for specificity of the syntactic positive shift.

One of the current issues in the investigation of language by means of event-related brain potentials (ERPs) is whether there is an ERP effect that can be specifically related to the processing of syntactic information. It has been claimed that a late positivity (P600 or SPS-syntactic positive shift) occurring to syntactic violations or ambiguities qualifies as such an effect. In the present investigation we compared ERPs elicited by morphosyntactic (case inflection errors), semantic, and orthographic (misspelled words) violations in a group of young German subjects. All three types of violations gave rise to late positivities having the characteristics of the previously described P600/SPS. In an earlier time window, however, semantic violations were associated with a centroparietally distributed N400 component, whereas syntactic violations gave rise to a negativity of smaller amplitude that had a frontocentral distribution. In light of the present experiment, the view that the P600/SPS as a whole reflects specific syntactic processes appears to be untenable and an alternative interpretation is proposed. The different distributions of the late positive shifts merit further investigation.

Adult↗