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T L Babb

Publications and source records attributed to T L Babb.

At least 91 records · Page 5Linked to original sources
PubMed1983

Visual receptive fields and response properties of neurons in human temporal lobe and visual pathways.

Recordings were made from depth electrodes placed in medial temporal and occipital lobes for the localization of seizure foci in patients with medically intractable psychomotor epilepsy. Electrodes were located in the amygdala and at three rostrocaudal levels of the hippocampal formation including the posterior hippocampal gyrus, which lies medial to the portion of the geniculostriate pathway which passes through the temporal lobe. 1. Approximately 10 per cent of single units recorded from microelectrodes chronically implanted in medial temporal sites were visually responsive. Some of the units in the posterior hippocampal gyrus displayed receptive field characteristics similar to those reported in lower primates, including circular or linear shape, monocular or binocular response, variable (1 to 10 deg) receptive field size, retinotopic organization and sustained or transient response. 2. Visually responsive units were also recorded from lateral geniculate nucleus, pulvinar nucleus and occipital cortex, and their basic response form and latencies compared with the short latency visually responsive cells in medial temporal lobe. 3. The heterogeneity of receptive field characteristics in the medial temporal lobe is consistent with the existence of more than one visual input to this region, while their retinotopic relationship differentiates these receptive fields from those of units studied in the inferior temporal lobe of lower primates. 4. Properties of visual pathways in this region are discussed in relation to several types of temporal lobe function and to memory. Recordings from these neurons offer a rare opportunity for comparison of central visual response properties and receptive field characteristics of humans with those reported in animal studies.

Adult↗
PubMed1982

Asymmetry and ventral course of the human geniculostriate pathway as determined by hippocampal visual evoked potentials and subsequent visual field defects after temporal lobectomy.

Twenty-two patients with psychomotor epilepsy were implanted with depth electrodes along the axis of the mesial temporal lobe to identify an operable unilateral epileptic focus. Neuronal and field potentials were recorded in response to diffuse retinal illumination and clear short-latency responses were found in parahippocampal gyrus. These visual afferents in the mesial temporal lobe are assumed to be both from subcortical and cortical visual areas. There was a clear asymmetry in the ventral trajectory of the geniculostriate pathway as evidenced by asymmetric neuronal and field potential responses to brief flashes in right vs. left hippocampal gyrus and confirmed by a corresponding partial visual field deficit following therapeutic anterior temporal lobectomy. These results demonstrate that there is a retinotopic organization of fibers in the human geniculostriate pathway and that this pathway may have considerable variability in the anterior and ventral course these fibers take through the temporal lobe. These findings adequately account for the presence of direct projections from geniculate to hippocampal cortex and for unexpected hemianopsias with standard resections of the temporal lobe when there is a deviant detour of the geniculostriate pathway.

Dominance, Cerebral↗
PubMed1981

Demonstration of caudally directed hippocampal efferents in the rat by intracellular injection of horseradish peroxidase.

Axonal projections of rat hippocampal neurons were demonstrated by intracellular injections of horseradish peroxidase. The data indicated a prominent caudally directed projection from pyramidal neurons of hippocampal field CA1, provided evidence that the subiculum is one of its targets, and suggested that the caudally directed efferents from CA1 are more numerous than rostrally directed ones.

Animals↗
PubMed1981

Neuronal firing patterns during the spread of an occipital lobe seizure to the temporal lobes in man.

Neuronal recordings from occipital cortex and hippocampus during a seizure originating in the occipital lobe of a patient with an occipito-temporal tumor demonstrated that the visual aura resulted from neuronal activation of medial peristriate and possibly other occipital lobe neurons while the psychomotor automatisms followed 10-20 sec later and were caused by recruitment of hippocampal neurons bilaterally. This confirmed that the complex seizure symptoms were caused by propagation from an occipital lobe focus. The psychomotor symptoms have not recurred for the 6 months since interruption of occipito-temporal connections; however, the spared medial occipital neurons still produce visual auras.

Astrocytoma↗
PubMed1980

Neurophysiology of the caudally directed hippocampal efferent system in the rat: projections to the subicular complex.

We studied the responses of rat subicular neurons to electrical stimulation of the hippocampus. Four main results were obtained: (1) orthodromic excitatory responses were recorded in neurons of the subicular complex following electrical stimulation of the ipsilateral hippocampus. Responses were usually characterized by a single action potential immediately followed by an inhibitory period. Intracellular recordings showed that spikes were triggered by EPSPs. Preliminary data indicated that the excitatory effects extend to the entorhinal cortex as well; (2) neither fornical nor commissural afferents were necessary for the responses; they were present even in animals that had received surgical sections of the fornix and hippocampal commissures prior to the neurophysiological experiments; (3) some neurons showed evidence of frequency potentiation when stimulated at 5/sec or 10/sec; and (4) neurons in hippocampal fields CA1 and CA3 with the physiological characteristics of pyramids could be antidromically activated by electrical stimulation of subicular white matter. The results indicate an excitatory, caudally directed hippocampal efferent system that originates in fields CA1 and CA3, and that projects to all ventrocaudal regions of the subicular complex.

Animals↗
PubMed1980

Inhibition in subicular and entorhinal principal neurons in response to electrical stimulation of the fornix and hippocampus.

We performed experiments studying the responses of rat subicular and entorhinal neurons to electrical stimulation of the fornix and hippocampus. Four main results were obtained: (1) extracellular recordings from principal neurons showed prolonged inhibition in response to stimulation, and intracellular recordings showed prominent IPSPs; (2) neither fornical nor commissural afferents were necessary for the inhibitory responses; they were present even in animals that had received prior surgical sections of the fornix and hippocampal commissures; (3) antidromic responses to fornix or hippocampal stimulation were recorded in neurons of the subicular complex; and (4) 3 cells in the subicular and entorhinal cortex were encountered that showed some of the properties associated with interneurons. The results suggest that principal neurons of the subicular complex share a number of properties with hippocampal pyramidal cells, including intrinsic recurrent inhibitory circuitry. Further study is required to determine the pathway for entorhinal inhibitory responses.

Animals↗
PubMed1980

A circuit for safe diagnostic electrical stimulation of the human brain.

An electronic circuit for controlled electrical stimulation of the human brain has been designed to optimize safety in charge transfer from electrodes to brain and to eliminate the likelihood of unwanted currents from the neurostimulator resulting from component failure. The circuit schematics feature the following designs: (1) a highly accurate and versatile rate generator 0.5 p.p.s. to 99 in increments of 0.5 p.p.s., (2) symmetrically-biphasic lead and lag pulses of 100 musec duration, (3) photo-isolated driver amplifiers with accurate waveform, reproduction, (4) true biphasic passive-current regulators driven by an isolated battery supply voltage for switch-selectable currents of 0.25 to 5 ma or variable current regulation, (5) accurate current and voltage waveform monitors that isolate the stimulating electrodes from the monitors, and (6) capacity-coupled outputs to guarantee no net D.C. component at the end of each biphasic pulse. Relay-switching circuits are also shown that allow sequential stimulation and recording from one or several electrodes. This neurostimulator has been in use for over two years without evidence of electrolytic damage at identifiable electrode tips. The utility of simultaneous stimulation of several different electrodes at safe charge levels is described.

Amygdala↗
PubMed1980

Effects of long-term raphe nucleus stimulation on chronic limbic seizures in monkeys.

Long-term electrical stimulation of the raphe nuclei was performed in two monkeys with chronic psychomotor seizures. The daily seizure rate was significantly reduced in one monkey when a stimulus charge of 0.1 microC was used, but not during a subsequent experiment using a 0.4 microC charge. A charge of 0.4 microC also failed to alter the frequency of limbic seizures in a second monkey. The raphe stimulation caused neural damage to the brain stems of both animals. The possible effect this damage may have had on the repeatability of the results suggests that long-term raphe stimulation, like some other neural prostheses, may have diminishing effectiveness over time.

Aluminum Hydroxide↗
PubMed1979

Procaine-induced seizures in epileptic monkeys with bilateral hippocampal foci.

Intravenous procaine HCl given at low doses (0.5-2.5 mg/kg) to two monkeys with bilateral alumina hippocampal foci depressed interictal spiking or had little effect. At 5.0 mg/kg unilateral limbic activation occurred. At 10.0 mg/kg unilateral or bilateral limbic activation and generalized seizures could be evoked within 3-10 min. At higher doses (15 and 20 mg/kg) bilateral limbic activation or brief (one min) generalized seizures occurred. The unilateral-onset psychomotor seizures were not identical to spontaneous psychomotor seizures, and the generalized seizures never occurred spontaneously in these monkeys. However, these results do indicate that procaine challenges may selectively activate limbic epileptogenic areas without activation of debilitating generalized tonic-clonic seizures.

Animals↗
PubMed1979

Activity of human hippocampal formation and amygdala neurons during sleep.

Fine wire microelectrodes were implanted for diagnostic purposes in 17 patients suffering from psychomotor epilepsy. Single- and multiunit activity during waking and natural nocturnal slow wave sleep and REM sleep was recorded in the hippocampus (n = 42), hippocampal gyrus (n = 53), and amygdala (n = 32). The firing rates of hippocampal gyrus units usually decreased during slow wave sleep and then increased to levels equal to or above waking during REM. In contrast, the firing rates of hippocampal neurons generally increased during slow wave sleep and fell to very low levels during REM. The amygdala presented a more mixed pattern. Since the projection from the hippocampal gyrus to hippocampus is excitatory, their opposite patterns during sleep suggest that the tonic firing patterns of HC neurons may be mainly the result of subcortical afferents.

Afferent Pathways↗
PubMed1979

Effects of chronic cerebellar stimulation on chronic limbic seizures in monkeys.

No influences of chronic cerebellar stimulation were found in 10 different controlled experiments in 5 different monkeys with chronic alumina-induced psychomotor seizures. The stimulation parameters used were comparable to those used in human epileptics, and continuous daily EEG and behavioral monitoring allowed all seizures to be measured for daily frequency and duration over the several weeks of the experiments. Nocturnal seizures were similarly quantified in 3 monkeys to verify that cerebellar stimulation did not affect them. Motor cortex potentials evoked by cerebellar pulses confirmed that the stimulations were activating the cerebellum throughout the experiments, and measures of electrode access resistance and impedance verified that the electrodes remained in contact with the cerebellum. In one monkey given phenobarbital medication, interictal morbid behavior appeared to be improved by chronic stimulation of either cerebellum or dorsolateral frontal cortex, thus indicating an arousal influence of brain stimulation not due to cerebellum per se.

Aluminum Hydroxide↗
PubMed1978

A sample and hold amplifier system for stimulus artifact suppression.

A sample and hold amplifier system has been described which is capable of eliminating stimulus artifacts from a variety of biological recordings which would otherwise be impossible to interpret during electrical stimulation. Factors contributing to the prolongation of stimulus artifact are discussed in relation to the design requirements of this system. The application of this artifact suppression circuit to monitoring EEG seizures during electrical stimulation is demonstrated.

Amplifiers, Electronic↗
PubMed1978

Activity of human hippocampal formation and amygdala neurons during memory testing.

Single and multiple unit recordings were made from fine wires stereotaxically implanted in the hippocampus (HC), hippocampal gyrus (HCG), and amygdala (Am) of psychomotor epileptics. During a series of memory and control tests presented on slides, 21 of 155 HCG units, 15 of 59 HC units, and 2 of 54 Am units showed what appeared to be simple phasic or tonic visual responses. Twenty-seven other units, found only in the HCG, changed firing only during slides requiring a choice ('choice units'). A given choice unit responded during choices indicated verbally or manually, and during tasks requiring recall of Recent Memory, various visual discriminations, and expressions of preference. Choice units were not affected by sensory stimulation or motor activity in contexts not requiring choice. Phasically inhibited choice units had higher firing rates and lower signal-to-noise ratios than tonically excited units. Whether an electrode recorded a choice unit was unrelated to if it recorded a response to hyperventilation, or was in an area of epileptic pathology. Recordings were also made during an interview lasting several hours and eliciting a wide range of behaviors. Five of the 131 HCG units fired in repeated extended bursts, at least 50 times background during recall of word pairs or of the patient's hospital room. The unit response did not occur during numerous control tasks possessing similar overt sensory, motor, and social concomitants, but not requiring Recent Memory.

Action Potentials↗