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Biomedical subjects

D B Linke

Publications and source records attributed to D B Linke.

At least 19 recordsLinked to original sources
PubMed1997

Patterns of language dominance in focal left and right hemisphere epilepsies: relation to MRI findings, EEG, sex, and age at onset of epilepsy.

The present study evaluates results of language testing during intracarotid amobarbital procedures in 167 patients with either left (LHE, n = 81) or right hemisphere epilepsies (RHE, n = 86). In both groups there was a high rate of deviance from complete left hemisphere dominance of 24 and 31%, respectively. Whilst complete right hemisphere or incomplete left hemisphere language dominance were the prominent atypical patterns in LHE, RHE was associated with either bilateral dominance or incomplete left dominance. In LHE, atypical language dominance was frequently associated with an extratemporal localization of lesions or epileptic foci. The age at onset of epilepsy and the degree of right hemisphere language dominance correlated significantly in LHE but not in RHE. Finally, atypical dominance in LHE but not in RHE was associated with poorer language and nonlanguage functions, the latter being negatively correlated with the degree of right hemisphere language dominance. Conclusions are: (1) The data contradict the assumption of equipotentiality and favor the supposition of a predetermined left hemisphere superiority in language processing. (2) Atypical language dominance in LHE can largely be explained in terms of a plasticity dependent language shift as a consequence of early left hemisphere epilepsies and lesions. (3) Atypical dominance patterns in RHE appear to reflect the prevalence of genetically determined variants and the possibility of a language transfer from the right to the left hemisphere.

Age of Onset↗
PubMed1994

Quantitative and qualitative evaluation of patterns of cerebral language dominance. An amobarbital study.

As a part of presurgical evaluation, 173 patients received bilateral intracarotid amobarbital tests for determination of cerebral language dominance. Language testing during intracarotid amobarbital procedures (IAP) consisted of the following tasks: automatic speech, sentence comprehension, body commands, naming, repetition, reading, and spontaneous speech. Patterns of cerebral language dominance were evaluated and discussed on five levels of analysis: (1) quantification of language dominance on the basis of a lateralization index derived from the total language scores in each IAP; (2) determination of five dominance subpatterns (left or right dominant, strongly bilateral, and incomplete left or right dominant) according to quantification performed on level (1) and clinical judgement; (3) qualitative differentiation of three kinds of bilaterality (positive, negative, and general) according to total language performance in left and right IAP; (4) analysis of grouped linguistic subfunctions extracted from performance in specific IAP subtests; (5) extraordinary individual case histories. The distribution of lateralization indices revealed only partially continuous degrees of lateralization, especially between the left-dominant and bilateral subgroups. As for the clinically oriented classification, incomplete left dominance is frequent (16.2%), while incomplete right dominance does not occur at all. Atypical dominance patterns are mostly correlated to bilateral and/or extratemporal foci. Concerning grouped subfunctions, a rotated factor matrix statistic yields an analysis of clusters of IAP subtests, where functions involving expressive language capacities are separated from those that are purely receptive. Further analyses of bilaterality subpatterns suggest that there are mainly four bilaterality phenomena, namely interhemispheric dissociation, double representation, unilateral representation of subfunctions, and partial representation of subfunctions in either hemisphere. Application of these differentiations to individual cases yields additional evidence that can be used in patient selection for operation in order to avoid postoperative neuropsychological deficits, especially in candidates for extratemporal surgery. In conclusion, a multilevel analysis of IAP language data is recommended since it permits a detailed account of varieties of language dominance patterns and contributes to more adequate presurgical decision-making in planned operations in cognitively relevant brain areas.

Adolescent↗
PubMed1994

Right hemisphere restitution of language and memory functions in right hemisphere language-dominant patients with left temporal lobe epilepsy.

Concomitant with the right hemispheric restitution of language functions after early left hemisphere lesions, suppression effects on originally right hemispheric visuospatial/constructional functions have repeatedly been reported. The present study evaluated this issue in 10 right hemisphere language-dominant patients with temporal lobe epilepsy. Left hemisphere language-dominant patients with left (n = 10) or right (n = 10) temporal lobe epilepsy served as controls. The following results were obtained: in all but one of the right dominant patients, left hemisphere lesions, left hemisphere foci and histories of early left brain damage indicated that secondary language transfer rather than a genetically determination is the more likely cause of the right hemisphere dominance. Despite this transfer, the language functions (comprehension, fluency, reasoning) of the right dominant patients remained significantly impaired. Language generally appeared to be better preserved in patients with an onset of epilepsy before the third year of life or a circumscribed left hemisphere lesion. No suppression effects could be detected on the level of complex cortical language and non-language functions. In contrast, on the level of temporo-limbic memory functions, verbal learning and recognition were left largely intact, albeit mostly at the expense of visuo-spatial learning and memory. The findings of the study thus indicate that the cerebral plasticity of the right hemisphere differs according to the extent of the left-hemisphere lesion, the onset of structural/functional damage and the complexity of the functions requiring restitution. Assuming that language and memory represent neocortical and palaeocortical functions, respectively, the restitution process is seemingly governed by their status in a phylogenetically determined hierarchy of functional importance.

Brain Diseases↗
PubMed1993

[Does lateralized hemispheric control of cardiovascular activity exist? A Wada test study].

The question of whether the influence of the cerebral hemispheres on cardiovascular activity exhibits left/right differences is important for the understanding of the psychophysiology of the autonomous nervous system. Experimental results have been contradictory. One experimental procedure used is the intracarotid amobarbital test (Wada test: short anesthesia of one cerebral hemisphere). Even with this test contradictory results have been obtained in various studies, although all involved relatively small of numbers of patients. Some authors have described increases in heart rate following anesthesia of the left hemisphere, while others found little or no effect at all. We therefore searched for evidence of lateralization in a larger number of patients (36) with complex partial seizures. These patients underwent the Wada test as part of the preoperative diagnostic evaluation. In this study, inactivation of the left or right hemisphere did not lead to significantly different effects on heart rate, or on systolic or diastolic blood pressure.

Adolescent↗
PubMed1992

Correlations between verbal memory performance and electrocorticographically determined suppression of electrical brain activity in intracarotid amobarbital tests.

As a part of presurgical evaluation, bilateral intracarotid amobarbital procedures (IAPs) were performed in 42 patients (84 tests) with long-standing, medically intractable complex-partial seizures. During the IAPs, electrocorticographic (ECoG) recording was carried out via bilaterally implanted subdural electrodes. Five distinct patterns of suppression of electrical brain activity were observed: (1) an isoelectric line; (2) a burst-suppression pattern; (3) polyphasic waves; (4) high-voltage beta; and (5) low-voltage beta activity. Further, two types of specific reactions of the epileptic focus were detectable: (1) spike-burst-suppression patterns (SBS; 11 left; 7 right; 6 in both IAPs) and amobarbital-induced spikes (7 left; 4 right). ECoG suppression patterns as well as SBS and spike induction showed great variability in duration and overall occurrence. To determine the influence of these amobarbital-induced ECoG changes on results of IAP memory testing, performance in a verbal learning task was analyzed according to the ECoG patterns predominant during encoding. In left IAPs, it was found that SBS at the beginning of or during encoding had a significant negative effect on verbal memory. In right IAPs, verbal memory performance improved significantly with the decline of ECoG suppression. Hence, verbal memory performance in IAPs is significantly affected by specific ECoG suppression patterns and activation of the epileptic focus.

Adolescent↗
PubMed1992

Interhemispheric dissociation of expressive and receptive language functions in patients with complex-partial seizures: an amobarbital study.

Bilateral intracarotid amobarbital procedures (IAP) were performed in 144 patients with medically intractable complex-partial seizures. As a result of language testing, 29 patients (20.1%) were found to have bilateral language representation to different degrees. In four (2.8%) of these patients--all right-handers with early onset of epilepsy and/or evidence of early brain damage--there was strong evidence of an interhemispheric dissociation of expressive and receptive language functions. Two of these patients had circumscribed temporal foci (one left, one right), and receptive language functions were represented in the hemisphere contralateral to the focus. One patient with a right frontal focus showed left-hemisphere dominance for expressive functions, while the fourth patient exhibited left-hemisphere dominance for receptive functions associated with a right temporo-parietal focus. It is argued that in these four cases the circumscribed functional and/or structural impairments have led to a shift of the anatomically associated language functions to the opposite hemisphere (rather than to neighboring regions of the same hemisphere). These findings substantiate the hypothesis that in special circumstances the anterior (expressive) language area can be located in one hemisphere and the posterior (receptive) area in the other.

Adolescent↗
PubMed1992

Linguistic perseveration in dominant-side intracarotid amobarbital tests.

148 patients with medically intractable complex-partial seizures received bilateral intracarotid amobarbital tests. In 21 patients (14.2%), there were inappropriate responses (intrusions: N = 10; perseverations: N = 11) to a series repetition task (counting backwards) given immediately before amobarbital injection. Five cases from the perseveration subgroup are discussed in detail. In these patients, linguistic perseveration occurred with left-sided amobarbital injection, although they were all found to have left hemispheric speech dominance according to language testing during the amobarbital procedure. It is argued that these perseverations are best explained as a right hemispheric continuation of a speech motor program previously initiated by the left hemisphere.

Adolescent↗
PubMed1992

[A case of apraxia and global aphasia without apraxia for axial body movement].

The case of a right handed 58 year old woman is presented who suffered an ischemic stroke after angiography following a vasospasm in the left internal carotid artery. The neuropsychological examination revealed global aphasia and severe apraxia for movements of the face and the extremities. However, the patient was able to carry out adequately axial movements to imitation and also to verbal command. These particular findings are discussed and explained within the context of the existing literature.

Aphasia↗
PubMed1992

[Are cognitive processes in a phase relation with 40 Hz EEG?].

A coherent EEG-rhythm occurring in the 40 Hz range has been shown to correlate with cognitive processes of attention in a large number of studies. We intended to evaluate whether this frequency is of specific functional significance, and whether it may represent a rhythm of excitability for cognitive processes. The model of a rhythm of excitability assumes the 40 Hz-EEG to be a timer and organizer for information processing. Event-related potentials of 12 healthy normal subjects were recorded in an experiment of attention (auditory click stimulation). In order to evaluate whether the phases of the 40 Hz-EEG represent a rhythm of excitability, responses to stimuli having similar phases at the beginning of the stimulus were selected and averaged. An effect of the different 40 Hz-phases could not be demonstrated on the amplitude and latency of N100 and P200, components of the event-related potential associated with information processing. These findings suggest that a possible timer for cognitive processes of attention is not linked to the phases of the 40 Hz-surface-EEG.

Adult↗
PubMed1991

The locked-in syndrome and the behaviorist epistemology of other minds.

In this paper, the problem of correct ascriptions of consciousness to patients in neurological intensive care medicine is explored as a special case of the general philosophical 'other minds problem'. It is argued that although clinical ascriptions of consciousness and coma are mostly based on behavioral evidence, a behaviorist epistemology of other minds is not likely to succeed. To illustrate this, the so-called 'total locked-in syndrome', in which preserved consciousness is combined with a total loss of motor abilities due to a lower ventral brain stem lesion, is presented as a touchstone for behaviorism. It is argued that this example of consciousness without behavioral expression does not disprove behaviorism specifically, but rather illustrates the need for a non-verificationist theory of other minds. It is further argued that a folk version of such a theory already underlies our factual ascriptions of consciousness in clinical contexts. Finally, a non-behaviorist theory of other minds for patients with total locked-in syndrome is outlined.

Behavior↗
PubMed1991

Severe negative emotional reactions in intracarotid sodium amytal procedures: further evidence for hemispheric asymmetries?

Intracarotid sodium amytal (ISA) procedures are commonly used to determine the lateralization of language and memory functions in presurgical evaluation of epileptic patients. Besides, they provide a means for studying putative hemispheric asymmetries in the organization of emotional behavior. In this study, we report the incidence of negative emotional reactions in eighty epileptic patients undergoing ISA procedures as a part of presurgical evaluation. There were only four such reactions in a total of 159 tests (2.5%), all in right-handed patients with left cerebral dominance for language functions. In one case, emotional outbursts occurred with barbiturization of the nondominant hemisphere. This observation invalidates the hypothesis that a loss of left-hemispheric functions generally leads to negative emotional reactions due to a right hemisphere specialization for the processing of negative emotions. Rather than pointing to fixed hemispheric asymmetries, our findings suggest that severe negative emotional reactions result from a flexible cognitive evaluation of the organism's overall situation.

Adult↗
PubMed1991

[The subject of death. On the current controversy about brain-oriented determination of death].

Recently new concepts of partial brain death have seriously challenged the well-established whole-brain definition of death. In the present paper, we propose a 4-level-model of death, which differentiates the levels of attribution, definition, criteria, and tests. It is argued that whole-brain concepts of death are susceptible to partial-brain oriented criticism, mainly because they do not provide a precise determination of the subject of death.

Brain↗
PubMed1990

Activation of the epileptic focus during intracarotid amobarbital test. Electrocorticographic registration via subdural electrodes.

During presurgical evaluation, bilateral intracarotid amobarbital tests were performed in 21 patients (42 tests) to establish the lateralization of cerebral speech dominance as well as memory function. All patients suffered from long-standing, medically intractable, complex partial seizures. Electrocorticographic recording during the investigation was carried out via bilaterally implanted subdural electrodes. The aim of the study was to assess amobarbital-induced effects on the primary epileptic focus, determined throughout presurgical evaluation. Following the application of amobarbital the primary epileptic focus was selectively activated in 10 and preferentially activated in 3 patients suffering from temporal lobe epilepsy. Specific responses of the primary epileptic focus consisted of: (i) induction of a spike-burst-suppression pattern, mainly in the mesio-basal aspects of the focal temporal lobe (n = 13); (ii) induction of spikes or sharp waves following contralateral intracarotid injection (n = 10); (iii) late induction of spikes or sharp waves following ipsilateral injection (n = 4); (iv) loss or marked reduction of drug-induced beta activity over the primary epileptic focus (n = 14) following ipsilateral or contralateral injection. In conclusion, electrocorticographic recording during the intracarotid amobarbital test contributes valuable information about the primary epileptic focus in a high proportion of patients.

Action Potentials↗
PubMed1990

Crossed cerebellar diaschisis in intracarotid sodium amytal procedures: a SPECT study.

Eight patients with drug-resistant complex-partial seizures were subjected to left- and right-sided intracarotid sodium amytal (ISA) procedures during preoperative investigations for surgical treatment. Regional changes of cerebral and cerebellar blood flow during barbiturization were measured by [99mTc]-HMPAO-SPECT. Crossed cerebellar diaschisis (CCD) was observed in 13 out of 16 tests (81%) as well as ipsilateral cerebral hypoperfusion (87%). Thus CCD occurred more frequently in ISA procedures than in previously studied patients with cerebral infarctions and tumors. Since intracarotid injections of sodium amytal lead to hypoperfusion mainly in those areas of the brain that are supplied by the middle cerebral artery, functional suppression of these regions is supposed to be one of the main preconditions of CCD. Our findings suggest that CCD as demonstrated by the SPECT-technique is a common phenomenon in ISA procedures.

Adolescent↗
PubMed1989

[Depth EEG and evoked potentials using an intravascular catheter electrode in the baboon].

Obtaining an intracranial EEG, as well as a depth recording of the somatosensory evoked potentials, via a vascular approach are described. Experimentally, a directable microcatheter was placed in the middle cerebral artery of baboons. Using the catheter guide wire as electrode, intracranial electrical activity was recorded from within the cerebral vessels. Significantly, depth recordings of the SEP showed waves of thalamic origin not present in surface recordings. Advantages of this method over surface recordings are the greater gain of information possible and, over other techniques of depth recording, the comparibly lesser invasiveness.

Animals↗