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T Grunwald

Publications and source records attributed to T Grunwald.

14 recordsLinked to original sources
PubMed1999

Real-time tracking of memory formation in the human rhinal cortex and hippocampus.

A fundamental question about human memory is which brain structures are involved, and when, in transforming experiences into memories. This experiment sought to identify neural correlates of memory formation with the use of intracerebral electrodes implanted in the brains of patients with temporal lobe epilepsy. Event-related potentials (ERPs) were recorded directly from the medial temporal lobe (MTL) as the patients studied single words. ERPs elicited by words subsequently recalled in a memory test were contrasted with ERPs elicited by unrecalled words. Memory formation was associated with distinct but interrelated ERP differences within the rhinal cortex and the hippocampus, which arose after about 300 and 500 milliseconds, respectively. These findings suggest that declarative memory formation is dissociable into subprocesses and sequentially organized within the MTL.

Adult↗
PubMed1999

Amobarbital effects on the posterior hippocampus during the intracarotid amobarbital test.

OBJECTIVE: To relate functional effects on the hippocampus during the intracarotid amobarbital test (IAT) to its direct perfusion with amobarbital. METHODS: In 17 patients with intractable temporal lobe epilepsy, 28 hemispheres were perfused with 2.3 mL of 10% solution of 200 mg amobarbital and 37 MBq 99mTc-hexamethylpropylene amine oxime (HMPAO). For evaluation of amobarbital effects, data were combined from stereo-EEG (S-EEG) recordings from intrahippocampal depth electrodes and high-resolution SPECT after intracarotid injection of HMPAO. RESULTS: Perfusion of the entire hippocampus was observed only in hemispheres with a fetal origin of the posterior cerebral artery (PCA). In 10 hemispheres, S-EEG recordings could not unequivocally be assigned to either the anterior or the posterior part of the hippocampus. In the remaining 18 hemispheres, only the two with a fetal type of PCA showed perfusion of the entire hippocampus. In both, hippocampal electrical activity changed under the influence of amobarbital but did not differ in anterior and posterior contacts. In 15 of 16 hemispheres in which SPECT demonstrated perfusion of the anterior hippocampus only, amobarbital injection resulted in significant S-EEG activity change in both the anterior and the posterior parts of the hippocampus. CONCLUSION: S-EEG effects on the posterior hippocampus during the IAT can occur without direct perfusion of those brain areas.

Adolescent↗
PubMed1999

Limbic P300s in temporal lobe epilepsy with and without Ammon's horn sclerosis.

Limbic P300 potentials can be recorded within the mesial temporal lobes of patients with temporal lobe epilepsy (TLE). To delineate possible mechanisms of their generation and pathological alteration, we analysed limbic P300s in 55 TLE patients with and 29 without Ammon's horn sclerosis (AHS) and correlated their amplitudes with neuronal cell counts in 30 histopathological specimens. Limbic P300 amplitudes were reduced on the side of the epileptogenic focus only in patients with AHS. Moreover, in AHS patients, limbic P300 latencies were prolonged bilaterally; and in patients with left-sided AHS, amplitudes were reduced bilaterally. Both findings suggest bilateral functional deficits in TLE with unilateral AHS. Limbic P300 areas correlated significantly with neuronal densities of dentate gyrus granule cells but not hippocampal pyramidal cells in the CA1-4 (cornu ammonis) subfields. This finding points to a potential mechanism for the bilateral effects of unilateral AHS as both dentate gyri exhibit strong reciprocal contralateral connectivity.

Adolescent↗
PubMed1999

Prediction of postoperative seizure control by hippocampal event-related potentials.

PURPOSE: In spite of unequivocal results of the presurgical evaluation, between 10 and 30% of patients with medial temporal lobe epilepsy (MTLE) do not become seizure free by temporal lobe surgery. Because event-related potentials (ERPs) recorded within the hippocampal formation have been shown to be sensitive to the epileptogenic process, we examined whether ERPs can help to improve the prediction of postoperative seizure control. METHODS: We recorded ERPs to words from bilateral intrahippocaampal electrodes by using a visual word-recognition paradigm in 70 patients with unilateral hippocampal pathology and related these measurements to seizure outcome after temporal lobe surgery. RESULTS: Words elicited N400 potentials, which were reduced in amplitude on repetition on the side contralateral to hippocampal sclerosis. This contralateral repetition effect, however, was significantly diminished in the group of patients who experienced seizure recurrence after the operation. Contralateral repetition effects thus permitted correct prediction of postoperative seizure control in 94% of all patients. CONCLUSIONS: Recording ERPs to words within the medial temporal lobes can improve the prediction of postoperative seizure control. Reduced repetition effects contralateral to the side of hippocampal sclerosis may indicate bilateral epileptogenicity.

Adolescent↗
PubMed1999

Clinical relevance of amygdala sclerosis in temporal lobe epilepsy.

OBJECT: The goal of this study was to define the incidence and clinical significance of amygdala sclerosis (AS) in patients with temporal lobe epilepsy (TLE). METHODS: Surgical specimens of the lateral amygdaloid nucleus and the hippocampus excised from 71 patients who were treated for medically intractable TLE were quantitatively evaluated using a computer-assisted image-analysis system and compared with 10 normal autopsy specimens. Densities of neurons and reactive astrocytes in the patients with TLE were correlated with clinical, neuropsychological, and depth-electroencephalography data. The neuron counts of the lateral amygdaloid nucleus did not correlate with various presumed etiological factors of TLE including hereditary seizures, birth complications, febrile convulsions, traumatic brain injury, infections, seizure semiology, and epileptological outcome. However, patient age at surgery was significantly higher (mean difference 10 years) when AS was present, as compared with patients without AS (p < 0.01). Seizure origin, as determined by using amygdalohippocampal depth electrodes, did not correlate with the presence or absence of AS. Neuropsychologically, there was a significant correlation between the neuronal densities of the lateral amygdaloid nucleus and both preoperative visual recognition and postoperative deterioration of short-term verbal memory performance (p < 0.05). CONCLUSIONS: Except for the relatively long history of epilepsy, the presence of AS is not associated with specific clinical or electrocorticographic features of mesial TLE. However, patients without AS are particularly at risk for deterioration of short-term verbal memory following amygdalohippocampectomy.

Adolescent↗
PubMed1998

Limbic ERPs predict verbal memory after left-sided hippocampectomy.

Surgical removal of the dominant medial temporal lobe regions runs a considerable risk of verbal memory deficits which may be compensated for postoperatively by corresponding regions in the non-dominant medial temporal lobe. We examined this possibility by recording event-related potentials (ERPs) to words from the medial temporal lobes of patients with left-sided temporal lobe epilepsy (TLE) undergoing presurgical evaluation. N400 amplitudes in the right anterior medial temporal lobe predicted the postoperative verbal recall performance of individual patients with surprising accuracy, indicating that intracranial recordings can be used to quantify the functional capacities of the right hemisphere that can compensate for the verbal memory deficits after loss of medial temporal lobe structures in the left hemisphere.

Adolescent↗
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↗
PubMed1997

Differential involvement of left temporolateral and temporomesial structures in verbal declarative learning and memory: evidence from temporal lobe epilepsy.

A wealth of animal and human research has pointed to a significant involvement of the temporal lobes in memory processing, and yet the different functional roles of temporal cortical vs. mesial structures remain unclear. We studied verbal declarative memory, by using a word list paradigm that differentiates among learning (immediate recall), memory (delayed recall), and recognition, in epilepsy patients being considered for surgical resection of the left temporal lobe. Verbal memory was evaluated preoperatively and during the recording of intracranial event related potentials and postoperatively after selective hippocampectomy, temporal cortical lesionectomy, or anterior two-thirds en bloc temporal lobe resection procedures. Preoperative differences in verbal memory performance as a function of differences in underlying neuropathology, concurrent event-related potentials, and specific patterns of postoperative memory impairments lead to converging evidence that verbal declarative memory relies on a synergistic interaction of at least two functionally distinct brain systems. Material-specific data acquisition, or working memory, is mediated by neocortical temporal structures, whereas long-term consolidation/retrieval is particularly mediated by temporomesial structures. In contrast to the left temporal neocortex, the function of the temporomesial system appears to be material nonspecific. Apparently, its preferential involvement in verbal memory is due to its close interaction with overlying neocortical structures that are specialized for language processing.

Adult↗
PubMed1997

Human temporal lobe potentials in verbal learning and memory processes.

Animal experiments and lesion studies have shown the importance of temporal lobe structures for language and memory. We recorded intracranial cognitive potentials from the human lateral and medial temporal lobe in 26 patients with temporal lobe epilepsy undergoing presurgical evaluation, using a word- and a picture-recognition paradigm. Neuropsychological testing included word fluency, verbal reasoning, sustained attention and a verbal learning memory test (VLMT), which was an adapted version of the Rey auditory verbal learning test. Word-specific N400-potentials elicited in the middle temporal gyrus of the dominant left hemisphere (LTL-N400) predicted immediate recall performance after learning, whereas N400s, elicited by words but not pictures in the left anterior medial temporal lobe (AMTL-N400), predicted delayed recall. The number of words that were learned but forgotten after a 30-min delay correlated only with N400s elicited by words in the left anterior medial temporal lobe. Thus, intracranial recordings indicated that different electrophysiological responses in different temporal lobe structures were linked to memory scores from specific neuropsychological tests.

Adolescent↗
PubMed1995

Alterations of intrahippocampal cognitive potentials in temporal lobe epilepsy.

During presurgical evaluation event-related potentials were recorded with depth electrodes located longitudinally within the hippocampus in 25 patients suffering from unilateral temporal lobe epilepsy. Rare stimuli in a visual oddball paradigm elicited a pronounced negativity ("NO") in the hippocampal body. Amplitudes were significantly reduced on the side of the primary epileptogenic area. Visual presentations of words in a recognition paradigm evoked an earlier negativity ("ENW") in anterior and a later negativity ("LNW") in posterior hippocampal structures. Both were sensitive for recognition effects and showed reduced amplitudes on the side of the primary epileptogenic area. Relating the differences of left and right hippocampal "NO" and "ENW" amplitudes proved to be a sensitive method for topological diagnosis and allowed a correct lateralization of the primary epileptogenic area in all patients. Amplitudes of the hippocampal ENW, evoked in the dominant hemisphere by first presentations, strongly correlated with the recognition rate, when the primary epileptogenic area was situated in the contralateral temporal lobe. This correlation was reduced by the presence of ipsilateral epileptogenic foci.

Adolescent↗