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Biomedical subjects

R P Lesser

Publications and source records attributed to R P Lesser.

At least 37 records · Page 2Linked to original sources
PubMed1997

Imaging of delta- and mu-opioid receptors in temporal lobe epilepsy by positron emission tomography.

The involvement of opioid neurotransmitter systems in seizure mechanisms is well documented. In previous positron emission tomography (PET) studies in patients with unilateral temporal lobe epilepsy, we have found evidence for differential regulation of the opioid-receptor subtypes. The present study extends our previous observations to delta-opioid receptors by using the delta-receptor-selective antagonist [11C]methylnaltrindole ([11C]MeNTI). Paired measurements of delta- and mu-opioid receptor binding and metabolic activity were performed with PET using [11C]MeNTI and [11C]carfentanil ([11C]CFN) and [18F]fluorodeoxyglucose ([18F]FDG), respectively. Binding of [11C]MeNTI and [11C]CFN increased and [18F]FDG uptake decreased in the temporal cortex (TC) ipsilateral to the focus. Decreases in [18F]FDG uptake were more widespread regionally than were increases in opioid receptors. Increases in the delta- and mu-receptor binding showed different regional patterns. Increases in mu-receptor binding were confined to the middle aspect of the inferior TC, whereas binding of delta receptors increased in the mid-inferior TC and anterior aspect of the middle and superior TC. The increase in delta receptors suggests their anticonvulsant action, as previously shown for the delta-receptor subtype, whereas the different regional pattern of receptor alterations suggest the distinct roles of different opioid-receptor subtypes in seizure phenomena.

Adult↗
PubMed1997

Neuronal generators of visual evoked potentials in humans: visual processing in the human cortex.

PURPOSE: We wished to define the localization of cortical generators of visual (pattern) evoked potentials (VEP) and the temporal sequence of activation in the occipital region. METHODS: In 4 candidates for epilepsy surgery, a large array of subdural electrodes was placed over occipital areas. Checkerboard pattern reversal stimuli were generated and the epileptogenic focus was localized and functionally mapped. Magnetic resonance imaging did not show any occipital lesions in any of the 4 patients. RESULTS: The area first activated was the lingual gyrus in the mesial occipital lobe (negative potential peaks at approximately 70 ms), followed by an area superior to the calcarine fissure (negative peaks at approximately 80 ms). Later (starting at approximately 90 ms), there were positive potentials over the occipital pole and lingual gyrus, followed by potentials at the lateral occipital lobe. CONCLUSIONS: These data support the idea that VEP are generated in the mesial and lateral occipital cortex by different circumscribed neuronal generators with different latencies of activation. The scalp-recorded N1 and P1 potential peaks most likely derive from the progressive activation of neuronal masses in different regions of the occipital lobe.

Brain Mapping↗
PubMed1996

An approach to seizure detection using an artificial neural network (ANN).

We have developed an EEG seizure detector based on an artificial neural network. The input layer of the ANN has 31 nodes quantifying the amplitude, slope, curvature, rhythmicity, and frequency components of EEG in a 2 sec epoch. The hidden layer has 30 nodes and the output layer has 8 nodes representing various patterns of EEG activity (e.g. seizure, muscle, noise, normal). The value of the output node representing seizure activity is averaged over 3 consecutive epochs and a seizure is declared when that average exceeds 0.65. Among 78 randomly selected files from 50 patients not in the original training set, the detector declared at least one seizure in 76% of 34 files containing seizures. It declared no seizures in 93% of 44 files not containing seizures. Four false detections during 4.1 h of recording yielded a false detection rate of 1.0/h. The detector can continuously process 40 channels of EEG with a 33 MHz 486 CPU. Although this method is still in its early stages of development, our results represent proof of the principle that ANN could be utilized to provide a practical approach for automatic, on-line, seizure detection.

Electroencephalography↗
PubMed1996

Treatment of epilepsy with multiple subpial transections: an acute histologic analysis in human subjects.

Multiple subpial transection (MST) is a new surgical technique for treating seizures that arise from functionally critical cortical areas. It has a reported efficacy comparable to that of standard temporal lobe resections. Although the mechanism through which MST works is unknown, the carefully controlled lesions, placed 5 mm apart at the midlevel of the cortical gyri, could produce fiber damage that would prevent horizontal synchronization and spread of epileptic discharges while allowing normal cortical functions such as those related to movement or speech to be preserved. We studied the acute neuropathological features associated with MST in 8 patients with intractable temporal lobe epilepsy. Transections were made along major temporal gyri just before standard lobectomy was performed. After resection, tissue was processed by conventional histological and immunocytochemical techniques. Macroscopically, subpial transections (STs) were perpendicular to the main gyral axis and had an appropriate spacing. Microscopically, most of the lesions were perpendicular and at midlevel. However, many transections involved the lateral aspects of the small gyri, resulting in oblique or deep STs, some of which reached the gray-white matter junction due to the complex microscopic neocortical architecture, in which small gyri are superimposed on major lobar gyri, and to the variable cortical thickness. Extensive acute pyknosis and tissue edema were also evident adjacent to the transections. These changes were variable and extenDed 1-3 mm laterally as irregular columnar blocks. In the deep lesions, myelin pallor and decreased neurofilament immunoreactivity were observed in the white matter. Based on the distribution of STs and their adjacent parenchymal injury, we conclude that this technique produces block-type lesions that probably disrupt propagation of epileptogenic activity. In most instances, midlevel horizontal fibers are damaged; one third of the cases showed additional deep injury that would sever afferent and efferent axons. Therefore, in addition to horizontal desynchronization, a deafferentation mechanism involving different fiber systems may contribute to the anti-seizure effects of MST. We hypothesize that preservation of cortical function is mediated by cortex remaining in the sulcus and gyral crown and possibly by reorganization of tissue adjacent to transections.

Adult↗
PubMed1996

Cognitive effects of resecting basal temporal language areas.

Electrical stimulation of the basal temporal region of the dominant hemisphere before partial temporal lobectomy for epilepsy sometimes produces temporary interruption of language function, but the significance of removal of this area is unknown. We evaluated the correlation between resection of the basal temporal language areas (BTLA) and certain types of postoperative language deficits. In a population of 25 patients, we mapped the inferolateral temporal lobe with cortical electrical stimulation, verifying the positions of the stimulating electrodes with three-dimensional computed tomography (CT). Eighty percent of the patients developed transient language deficits with stimulation, particularly with tests of confrontation naming and comprehension. BTLA was primarily located in the fusiform gyrus, from 1 to 9 cm from the temporal tip. At testing 6-12 months after operation, patients with BTLA resection performed worse (mean 9% decrease) than those with no BTLA resection (mean 4% improvement) on tests of confrontation naming (p = 0.03). Resection size accounted for less of the variance in decrease in confrontation naming than did resection of the BTLA. Tests of performance I.Q. (PIQ), verbal I.Q. (VIQ), or recognition memory for word and verbal learning showed no significant difference between these groups. Most patients do not have language decrease with removal of basal temporal lobe 5-6 cm from the tip, even with removal of BTLA. Some patients, however, have persistent decrease in naming.

Adolescent↗
PubMed1996

Does the central sulcus divide motor and sensory functions? Cortical mapping of human hand areas as revealed by electrical stimulation through subdural grid electrodes.

To clarify the exact anatomic relationship of electrically identified hand areas to the central sulcus, we constructed cortical surface renderings of magnetic resonance images (MRI) to locate the central sulcus accurately and measured the distances of stimulated points from the central sulcus and the Sylvian fissure. We obtained hand responses in 33 patients who underwent implantation of subdural grid electrodes for evaluation and surgical treatment of intractable epilepsy and analyzed these responses according to the presence of motor, sensory, mixed motor and sensory, and arrest responses. Hand motor responses occurred not only in the precentral gyrus but also in the postcentral gyrus, with great variability in superior-to-inferior distribution. Sensory responses also occurred in both the precentral and postcentral gyri with a distribution more ventral than that of motor responses. Mixed motor and sensory responses tended to be limited to the middle part of the central sulcus. Sites where electrical stimulation arrested simple hand repetitive voluntary movements occurred widely throughout the premotor and primary sensorimotor cortices. These data indicate a marked variability in the location of the human cortical hand area, and suggest that motor and sensory hand cortices overlap and are not divided in a simple manner by the central sulcus.

Brain Mapping↗
PubMed1995

Auditory speech processing in the left temporal lobe: an electrical interference study.

Auditory syllable discrimination, identification, and comprehension were investigated by direct cortical electrical interference in three patients with indwelling subdural electrode arrays. Without electrical interference, patients performed similarly to matched normal subjects. With electrical interference, selective deficits were observed in the posterior superior temporal (PST) lobes of all three patients. At specific PST sites, only comprehension was impaired, while at proximal sites comprehension and identification were impaired, but discrimination remained intact. At a single PST site, all three auditory speech functions were impaired. These findings suggest that lower-level auditory speech functions can operate independent of higher-level processes, as claimed by traditional hierarchical models. However, analysis of discrimination errors revealed lexical-semantic and phonological effects, suggesting that higher-level functions also influence lower-level processing. These data can be explained by a bidirectional processing model, with differentially weighted connections.

Adolescent↗
PubMed1995

It is not harmful for patients with epilepsy to view their own seizures.

Having a seizure in public is a concern to people with epilepsy and can represent a barrier to psychosocial adjustment. Seeing his or her own seizures might help the patient deal with seizures more realistically, but also could be emotionally detrimental. We therefore showed patients videos of their own seizures before their discharge from our inpatient epilepsy monitoring unit. One of the investigators was present to answer questions. The Spielberger State Trait Anxiety Scale (SSTAS) was administered before and after viewing and 1 month later together with a questionnaire related to the patients' feelings and attitudes about viewing their own seizures. Results using one-way repeated-measures multivariate analysis of variance (MANOVA) showed no differences for the items in the pre- and posttest questionnaire. For the SSTAS, no significant differences were detected among the pretest and the two posttests by one-way repeated ANOVA (p = 0.10). These results suggest that it is not harmful to view one's own seizures in a controlled setting.

Adaptation, Psychological↗
PubMed1995

Brainstem auditory evoked potentials recorded around the human upper brainstem area.

The intracranial spatiotemporal distributions of brainstem auditory evoked potentials were analyzed in two patients with epilepsy to study the dipole directions of waves III and V, previously found to have a horizontal and a vertical dipole, respectively. Depth electrodes were implanted bilaterally into the frontal and temporal lobes of these patients, the targets including the amygdala and hippocampus which are close to the upper pons and midbrain. Recordings around the upper pons and from the subcortical area downwards along the dorsal aspect of the upper pons indicated that waves III and V are constructed of mixed dipoles, wave III also having a vertical dipole segment and wave V also a horizontal one. These results suggest that several neural activities from the upper pons to midbrain contribute to the generation of waves III and V.

Adult↗
PubMed1994

Practical detection of epileptiform discharges (EDs) in the EEG using an artificial neural network: a comparison of raw and parameterized EEG data.

We have developed and tested "off-line" an artificial neural network (ANN) that successfully detects epileptiform discharges (EDs) when trained on EEG records marked by an electroencephalographer (EEGer). The system was trained on both parameterized and raw EEG data and can process 49 channels of EEG data in real time on an 80486/33 MHz personal computer, making it capable of processing EEG on-line in long-term monitoring units. Our detector consists of 2 stages: (1) a threshold detector identifies candidate EDs in 4-channel bipolar chains within the recording montage, parameterizes them and then passes these data to the second stage; (2) a 3-layer feed-forward ANN decides if a candidate wave form is an ED. The intersection of detector sensitivity and selectivity curves, or crossover threshold, for 10 patients from our Epilepsy Monitoring Unit occurred at 73% for parameterized EEG data and at 46% for "raw" EEG data. The ANN could be adapted to different EEGers' styles by changing the ANN output threshold for accepting candidate wave forms as EDs. In this "proof of principle" study the detector was trained on EEGs from 10 Johns Hopkins Hospital Epilepsy Monitoring Unit (JHH EMU) patients. We used different EEGs from the same patients for testing. Current testing should demonstrate that the ANN detector can generalize to previously "unseen" patients. This study shows that ANNs offer a practical solution for automated, real time ED detection that uses, standard, inexpensive computers, is easily adjustable to individual EEGer style and can produce sensitivities and selectivities similar to those of EEGers.

Brain↗
PubMed1994

Cortical tongue area studied by chronically implanted subdural electrodes--with special reference to parietal motor and frontal sensory responses.

Motor and sensory cortical tongue representations were examined in 40 patients with intractable seizures who underwent chronic subdural electrode grid implantation. Tongue responses were observed in a wide area 4.5 cm anterior and 3 cm posterior to the central sulcus. The distribution of the responses was not influenced by whether the responses were unilateral or bilateral. In patients with fronto-parietal lesions, the tongue motor area was located significantly more superior to the Sylvian fissure and more anterior to the central sulcus than was the tongue motor area of patients without organic lesion. Both motor and sensory responses were found outside of the classic precentral or postcentral area on the lateral surface of the cortex. Motor responses ('parietal motor responses') could occur posterior to the central sulcus and, rarely, sensory responses ('frontal sensory responses') were identified anterior to the central sulcus. These paradoxical parietal motor and frontal sensory responses were seen in 17 out of 40 (42.5%) patients. Nine of these 17 patients had no organic brain lesion on MRI. Clinical factors, such as patient's age, duration of seizures and cognitive functions (IQ, word fluency score), did not influence the frequency of the paradoxical responses. However, patients with brain lesions showed a tendency to have associated paradoxical responses (P < 0.05). In conclusion, paradoxical responses are not uncommon in epilepsy patients, particularly in those with organic lesions. The physiological and clinical implications of the paradoxical responses are discussed.

Adolescent↗
PubMed1994

Reliability of amygdalohippocampal volume measured directly on MRI films.

Volume measurement of the amygdalohippocampus on MRI may provide important information for epilepsy surgery. This study investigated the reliability of direct volume assessment (DVA) versus computer-assisted measurement (CAM) of amygdalohippocampus. DVA was carried out by counting the number of squares occupied by amygdalohippocampus in a transparent mm2 overlay used on both sagittal and coronal films. CAM was achieved using the 'thresholding and tracing' automated technique. Seventeen patients undergoing language-dominant left temporal lobectomy were studied. Mean volume as determined by the CAM was 4.99 +/- 1.31. In DVA, the mean volume was 5.05 +/- 1.23 (r = 0.974). Reproducibility of the volume measurement was tested by repeating measurements 5 times on 5 patient samples of amygdalohippocampal complex in DVA, and 3 times on 4 samples in CAM. The mean coefficient of variation for amygdalohippocampal volume was 6.9 +/- 3.2% in DVA and 3.9 +/- 2.0 in CAM. We also tested a more simplified method of assessing amygdalohippocampal volume by calculating the left to right volume ratio from MRI scans (2-40 films for each sample). Volume ratios determined directly from MRI films made in different months (14 samples) and of different sections (coronal and sagittal series, 18 samples) correlated well with each other (p < 0.01). Direct assessment of amygdalohippocampal volume can be used effectively for preoperative evaluation of the patient with epilepsy.

Adult↗
PubMed1994

Long-term monitoring with digital technology for epilepsy.

The use of video-electroencephalography for the evaluation of children is reserved for inpatients with intractable "seizures." Prolonged video-electroencephalographic monitoring is used to ascertain whether the events are epileptic in nature, or to evaluate the medically intractable patient with epilepsy for surgical management of seizures. The increasing interest in the evaluation of patients with intractable epilepsy and recent technologic advances have led to a greater sophistication and versatility in patient evaluation. This paper reviews currently available technologies and newer digital acquisition and playback systems, and discusses ways of optimizing the evaluation of patients with intractable seizures.

Adult↗
PubMed1994

Distribution in time of seizures during presurgical EEG monitoring.

We studied the length of stay needed to record a certain number of seizures in a highly selected group of patients with intractable epilepsy in the final stages of presurgical monitoring. The mean length of stay needed to record one seizure was 2.9 to 3.7 days, depending on the recording technique, 4.5 to 5.5 monitoring days to record three seizures, and 6.1 to 7.6 days to record five seizures. It took 5 days to record at least one seizure in 90% of patients, 7 to 10 days to record three seizures, and 8 to 12 days to record five seizures. One-third of all patients had fewer than five seizures during their stay. Extrapolating from the results in our unit, we computed a need for 91 to 227 presurgical epilepsy monitoring beds to evaluate 2,000 to 5,000 similar epilepsy surgery candidates requiring invasive monitoring in the United States each year. Additional beds would be needed to monitor patients admitted for other purposes.

Adolescent↗
PubMed1994

The role of epilepsy centers in delivering care to patients with intractable epilepsy.

Epilepsy is a disorder that can profoundly influence people's ability to participate fully in society. To ameliorate the effects of the disorder, the health care system should provide mechanisms that explicitly facilitate consultations among primary-, secondary-, and tertiary-level health care providers. Second, it should develop schedules for compensating for both the less and the more technologically intensive methods of diagnosis and treatment. These should allow improved or complete seizure control in a significant portion of patients with intractable seizures. Although there are costs for such changes, the costs of not making them may be higher.

Delivery of Health Care↗
PubMed1994

Proton MR spectroscopy in patients with seizure disorders.

PURPOSE: To evaluate the ability of proton MR spectroscopy to detect metabolic abnormalities in the seizure focus of humans with epilepsy. METHODS: Single-voxel MR spectroscopy and MR imaging was performed in a group of 13 patients with a variety of seizure disorders and in the temporal lobes of 14 healthy volunteers. Signals from choline, creatine, N-acetyl-L-aspartate, and lactate were quantitated in both the epileptogenic focus and the contralateral brain region. RESULTS: In normal temporal lobe, concentrations of choline, creatine, and N-acetyl-L-aspartate were 2.0 +/- 0.7, 7.8 +/- 1.9, and 11.0 +/- 2.1 mumol/g wet weight, respectively, with no detectable lactate. In all patients, a reduction in the N-acetyl-L-aspartate signal was observed in the electrically defined (scalp electroencephalogram) seizure focus compared with the mirror-image contralateral side. Lactate was elevated only in patients who had seizures during or immediately before the MR examination. Seven of 13 patients studied had normal MR examinations. CONCLUSIONS: Proton spectroscopy demonstrates alterations in N-acetyl-L-aspartate and lactate levels that can be used to locate the epileptogenic focus and may be a useful adjunctive diagnostic technique for the evaluation of patients with seizures who are eligible for resective surgery.

Adolescent↗