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Biomedical subjects

M J O'Connor

Publications and source records attributed to M J O'Connor.

At least 19 recordsLinked to original sources
PubMed1992

The functional relationship between antidromically evoked field responses of the dentate gyrus and mossy fiber reorganization in temporal lobe epileptic patients.

Field recordings from the dentate granule cell layer of in vitro brain slices of temporal lobe epileptic patients were evoked by antidromic stimulation. Tissue from the same specimen was stained by the Timm-sulfide method to assess the pattern and degree of mossy fiber reorganization into the supragranular layer. A wide range of physiological responses and Timm staining patterns was present across patients. A significant correlation was observed between the abnormality of antidromic responses, reflected by multiple secondary population spikes, and the degree of Timm staining of the supragranular layer. This relationship lends support to the hypothesis that mossy fiber synapses located in the supragranular layer may have functional implications for granule cell excitability in human epileptic tissue.

Adolescent↗
PubMed1992

Presurgical electroencephalographic patterns and outcome from anterior temporal lobectomy.

We reviewed data from 48 patients after anterior temporal lobe resection for medically intractable epilepsy. All had ictal electro-encephalographic (EEG) evidence of unilateral temporal lobe onset. Depth electrodes were used in 19 patients. Successful surgical outcome correlated significantly with factors that suggested a temporal lobe focus, particularly in the interictal scalp EEG. The most successful outcome occurred in patients with well-localized unilateral interictal temporal spikes (100% improved). The group with well-localized bilateral temporal spikes also did well (76% improved). Patients with extratemporal spread of the interictal spike on scalp EEG, either unilaterally or bilaterally, did less well. Only one third improved, despite extensive extracranial and intracranial monitoring, when indicated. The interictal scalp EEG may be the only EEG necessary for the presurgical evaluation of selected patients with intractable temporal lobe epilepsy.

Adolescent↗
PubMed1992

Cardiac rhythm during temporal lobe seizures.

We studied the neuroanatomic correlates of ictal tachycardia in 27 seizures from five patients with unilateral temporal lobe epilepsy being evaluated with bilateral temporal lobe depth electrodes and orbitofrontal subdural electrodes. There were 11 complex partial seizures, three simple partial seizures, and 13 subclinical seizures. For all seizures, heart rate (HR) increased in a graded fashion as new cortical regions anywhere in the brain were recruited into the seizure. HR plateaued at the new level despite EEG frequency changes until the next region became involved. Increases in HR did not correlate with increased duration of seizures but rather with volume of brain involved. Restricted amygdaloid seizure activity was generally insufficient to alter HR. We conclude that the amygdala has a limited role in modulating HR during seizures, and ictal tachycardia depends principally on the volume of cerebral structures recruited into a seizure.

Adult↗
PubMed1992

A noninvasive protocol for anterior temporal lobectomy.

We report the results of a protocol for choosing candidates for temporal lobectomy using a standard battery of objective tests without intracranial electrodes. We assigned each test a level of importance, and an algorithm was used to determine whether temporal lobectomy could be performed. Fifty-one patients (total pool, 103 patients) met protocol requirements and had an anterior temporal lobectomy with a mean follow-up of 39.4 months (range, 21 to 64 months), most remaining on anticonvulsant therapy. Eighty percent are seizure free, 12% have less than 3 seizures per year or only nocturnal seizures, and 8% have greater than 80% reduction in seizure frequency. One-third of patients who failed protocol criteria did not have temporal lobe seizures when studied with intracranial electrodes. We analyzed and modified the algorithm after comparing these patients with others who were poor candidates for temporal lobectomy. We conclude that this protocol is effective and recommend using such an objective algorithm.

Action Potentials↗
PubMed1991

NMDA receptor activation during epileptiform responses in the dentate gyrus of epileptic patients.

We previously showed that a low frequency (1 Hz) train of perforant path stimulation evokes burst discharges in the dentate gyrus of hippocampal slices obtained from patients surgically treated for intractable temporal lobe epilepsy. We report here that multiple population spikes that characterize the burst discharge are blocked reversibly by the specific NMDA receptor antagonist, D-(-)-2-amino-5-phosphonovaleric acid (D-APV). The epileptiform discharge evoked in human dentate gyrus by stimulation trains of 1 Hz could be reproduced in the rat dentate gyrus in vitro by the same stimulation protocol but required the presence of low concentrations (0.2-0.6 mM) of extracellular magnesium. We suggest that low frequency orthodromic stimulation of dentate granule cells through the perforant path progressively evokes an increase in the activation of NMDA receptors resulting in burst discharges in tissue from epileptic patients.

2-Amino-5-phosphonovalerate↗
PubMed1991

Acute effect of anterior temporal lobectomy on musical processing.

Patients with intractable epilepsy treated by anterior temporal lobectomy (Right, RT, n = 12; Left, LT, n = 9) and healthy controls (n = 12) with no musical training were prospectively evaluated with a standardized battery, including the Musical Aptitude Profile and the Seashore Tonal Memory Test. Before surgery, patients performed below controls (P less than 0.001), but there were no differences between RT and LT patients. After resection (2 weeks), RT patients showed a differential decline on tasks measuring perception of meter (P = 0.005) and tempo (P = 0.008) but not tonal processes. LT, and controls studied at the same time interval, showed no decline. The results support the role of the right hemisphere in specific aspects of musical processing.

Adult↗
PubMed1979

Cryptococcal granuloma presenting as an intracranial mass.

A case of cryptococcosis of the central nervous system presenting as an intracranial space occupying lesion is described. The world literature and epidemiology of this unusual disease are surveyed. Problems in the diagnosis and the use of modern diagnostic techniques are discussed. The authors suggest that cryptococcosis should be included in the differential diagnosis of an intracranial space occupying lesion.

Adult↗
PubMed1977

Regions of cerebral ischemia located by pyridine nucleotide fluorescence.

The fluorescence of the reduced form of the endogenous pyridine nucleotide nicotinamide adenine dinucleotide was used to map regions of ischemia in cat brain. A remarkably microheterogeneous pattern of increased fluorescence resulted from a critical level of incomplete cerebral ischemia. The fluorescence pattern suggests that ischemia occurs initially in microwatershed zones between penetrating cerebral arteries.

Animals↗
PubMed1977

Correlation of cerebral blood flow with outcome in head injured patients.

In order to determine the relationship of cerebral blood flow (CBF) to the clinical outcome of head injury, serial determinations of CBF were performed by the intravenous Xenon technique in 24 patients. The patients were of mixed injury severity and were classified into four groups depending on the neurological exam at the time of each CBF study. All eight patients who were lethargic on admission demonstrated increases in their minimally depressed CBF as they improved to normal status. Eleven patients in deep stupor or coma ultimately recovered. Ten of these patients initially had moderate to profound decreases in CBF which improved as recovery occurred. The single exception was an adolescent whose initial CBF was high but became normal at recovery. Five comatose patients died. In four of these, already depressed CBF fell even lower, while one adolescent with initially increased CBF developed very low CBF preterminally. The data presented in this report demonstrated a good correlation between CBF and clinical outcome. In every one of the adult survivors, depressed CBF increased as the patient recovered to normal status. All adults who died showed a deterioration of CBF as the neurological status worsened. The only exceptions were two adolescents who initially showed high CBF values. In the adolescent who died, CBF dropped to low levels while in the survivor a normal CBF was achieved. Thus in adults a traumatic brain injury was associated with depressed CBF which increased with recovery or decreased further with deterioration while the reaction to injury was quite different in the younger brain.

Adolescent↗
PubMed1977

Extracorporeal circulation (ECMO) in neonatal respiratory failure.

Sixteen moribund newborn infants with respiratory failure were treated with extracorporeal membrane oxygenation (ECMO) for 1 to 8 days. Cannulation via the right jugular vein and carotid artery was used to establish venoarterial-cardiopulmonary bypass. High flow (80 percent of cardiac output) allowed decreasing FIO2 and airway pressure. Diagnoses and results were as follows: respiratory distress syndrome, four patients (two improved, one survived); meconium aspiration syndrome, eight patients (four improved, three survived); persistent fetal circulation (some with diaphragmatic hernia), four patients (three improved, two survived). Intracranial bleeding occurred in 43 percent, accounting for most of the deaths. In a parallel series of 21 infants treated with conventional ventilator therapy, the mortality rate was 90 percent and intracranial bleeding occurred in 57 percent. ECMO provided life support and gains time in newborn respiratory failure. In high mortality risk infants, the rate of survival is higher and intracranial bleeding lower with ECMO than with optimal ventilator management.

Cerebral Hemorrhage↗
PubMed1975

Comparison of two methods of postoperative pulmonary care.

A new apparatus for postoperative pulmonary care was compared to one in common use. Vital capacity, a common clinical indicator of pulmonary status in the postoperative patient, was used as an index of improvement or deterioration. In patients using the device with increased dead space and expiratory pressure, there was a significantly greater increase in vital capacity than in those of the group who used blow bottles. Since increased vital capacity is indicative of improved pulmonary function, it is suggested that the use of the dead space-expiratory pressure device should result in a decreased incidence of postoperative pulmonary complications.

Humans↗
PubMed1975

Task characteristics and a stage 6 sensorimotor problem.

A previously demonstrated high rate of failure on a Stage 6 sensorimotor means-end problem, of children otherwise inferred to be in Stage 6 development, prompted a study of task characteristics of the problem. A component part of the task was modified by introducing an additional visual cue; the purpose of the problem was unchanged. Results indicated that problem solving was facilitated in the transformed condition, with older subjects performing somewhat better than younger subjects. The authors suggest that cognitive requirements of the problem, as representative of Stage 6 sensorimotor development, remained the same in the original or transformed condition. The modification appeared to permit children to focus their attention on the requirements of the problem, so that a greater number of children demonstrated mental representation. Task characteristics of sensorimotor problems need to be investigated further.

Age Factors↗