PubMed Health⌕ Search

Biomedical subjects

C A Robbins

Publications and source records attributed to C A Robbins.

33 records · Page 2Linked to original sources
PubMed1982

Operant conditioning of single unit activity in parietal cortex.

Two rhesus monkeys were trained to control firing patterns of single neurons in parietal cortex (areas 1, 2, 3, 5, 7) using an operant task previously applied to the study of precentral units. Twenty-four of 56 (43%) postcentral cells were controlled in contrast to 71 of 136 (52%) precentral units from these and 4 other rhesus monkeys. In addition, monkeys were able to drive precentral units to more sustained tonic firing rates than they could parietal units. An analysis of interspike interval (ISI) distributions showed that, in contrast to precentral units with modal ISIs of 25-50 ms, 50% of parietal units have modal ISIs of 2 ms. Such short ISIs may account for fewer postcentral units reaching control criteria for this particular operant task. Other factors that may contribute to the reduced control of postcentral cells are discussed, particularly the more complex afferent connections to parietal units when compared to precentral pyramidal tract neurons. The data indirectly support conclusions from previous studies that imply that operant control of cortical units is peripherally mediated and does not primarily involve a 'central' or 'open loop' system.

Action Potentials↗
PubMed1980

Operant control of precentral neurons: bilateral single unit conditioning.

Two Macaca mulatta monkeys were reinforced to operantly control a precentral neuron's firing pattern while a contralateral unit was monitored simultaneously. The results from 38 complete experiments indicate the following: (a) upon altering to the operant task, both the contingent and the non-contingent neurons changed firing patterns from preconditioning levels. However, as the monkey brought the contingent unit under operant control, there were no significant changes in the firing pattern of the non-contingent neuron; (b) when the contingencies were reversed so that the monkeys were reinforced to control the originally non-contingent neuron, the firing pattern off the originally contingent neuron returned to near baseline levels. These data indicate that although many precentral units may change firing patterns when the monkey attends to the operant task, the reinforced changes in firing pattern are not the result of a generalized phenomenon at the spinal level.

Animals↗
PubMed1980

Operant control of precentral neurons: control of modal interspike intervals.

The objects of these experiments were: (a) to determine modal interspike intervals (ISIs) of precentral cells involved in repetitious, gross motor movements; (b) to compare those modal ISIs to the modal ISIs of similar neurons under operant control; and (c) to determine if monkeys could change the modal ISIs of operantly controlled precentral neurons. Data were obtained from 4 monkeys conditioned to produce tonic firing of precentral neurons and one monkey trained to produce repetitious movements of the neck and contralateral limbs. Results are: (a) the modal ISIs from operantly controlled precentral units do not differ significantly from precentral neurons involved in repetitive gross motor movements; and (b) while under operant control, the monkeys cannot modify significantly the modal ISI of the majority of precentral neurons.

Animals↗
PubMed1979

Operant control of precentral neurons in monkeys: evidence against open loop control.

Four normal monkeys were operantly conditioned to change the firing pattern of 111 precentral neurons from phasic to tonic using an operant paradigm which quantifies the control of single neurons. Two monkeys then had their contralateral pyramidal tract (PT) sectioned and one monkey had C5-7 ventral rhizotomies. Postlesion data were: (1) contralateral C1-2PT lesions did not encumber the monkeys' control of precentral PTNs: (2) contralateral C5-7 ventral rhizotomies completely abolished accurate control of precentral neurons which received proprioceptive feedback from flaccid arm regions. These results indicate that precentral neurons are operantly controlled through proprioceptive feedback from peripheral mechanoreceptors. The output of the mechanoreceptors is probably dependent upon discrete joint angles and/or muscle tension which is maintained through non-PT pathways. These data do not support the concept that precentral neurons are operantly controlled directly from a central; 'open loop', pathway.

Animals↗
PubMed1979

EEG operant conditioning for control of epilepsy.

We report the results of 23 severely epileptic patients who were given EEG feedback training. The paradigm reinforced the patients' 18 Hz activity over the scalp approximation of their focus while suppressing temporalis EMG and low frequency EEG activity. In contrast to other studies using EEG feedback, only 43% of patients showed significant changes in seizure occurrence and a lesser number were felt to have benefited clinically. None of our neuropsychological test parameters were helpful in identifying (prospectively or retrospectively) patients most likely to respond to this treatment. Although a few patients were significantly helped by this training, the mechanism for this effect is unclear.

Adolescent↗
PubMedDate not supplied

BOLD-fMRI of PTZ-induced seizures in rats.

PURPOSE: To develop a non-invasive method for exploring seizure initiation and propagation in the brain of intact experimental animals. METHODS: We have developed and applied a model-independent statistical method--Hierarchical Cluster Analysis (HCA)--for analyzing BOLD-fMRI data following administration of pentylenetetrazol (PTZ) to intact rats. HCA clusters voxels into groups that share similar time courses and magnitudes of signal change, without any assumptions about when and/or where the seizure begins. RESULTS: Epileptiform spiking activity was monitored by EEG (outside the magnet) following intravenous PTZ (IV-PTZ; n=4) or intraperitoneal PTZ administration (IP-PTZ; n=5). Onset of cortical spiking first occurred at 29+/-16 s (IV-PTZ) and 147+/-29 s (IP-PTZ) following drug delivery. HCA of fMRI data following IV-PTZ (n=4) demonstrated a single dominant cluster, involving the majority of the brain and first activating at 27+/-23s. In contrast, IP-PTZ produced multiple, relatively small, clusters with heterogeneous time courses that varied markedly across animals (n=5); activation of the first cluster (involving cortex) occurred at 130+/-59 s. With both routes of PTZ administration, the timing of the fMRI signal increase correlated with onset of EEG spiking. CONCLUSIONS: These experiments demonstrate that fMRI activity associated with seizure activity can be analyzed with a model-independent statistical method. HCA indicated that seizure initiation in the IV- and IP-PTZ models involves multiple regions of sensitivity that vary with route of drug administration and that show significant variability across animal subjects. Even given this heterogeneity, fMRI shows clear differences that are not apparent with typical EEG monitoring procedures, in the activation patterns between IV and IP-PTZ models. These results suggest that fMRI can be used to assess different models and patterns of seizure activation.

Animals↗
PubMedDate not supplied

Predictors of medication noncompliance in a sample of older adults.

The subjects were 1028 respondents from a randomly selected sample of independently living adults aged 55 years and older in the southeastern United States. Data on background characteristics, physical health, life satisfaction, psychological distress, and medication compliance were gathered from structured interviews. Among the 785 subjects in the analysis who were taking prescribed medications, 75% were women, 83% were white, their median income was $12,500 annually, 66% lived alone, their mean age was 73.9 years, and their mean number of years of education was 11.4. Twenty-one percent of all respondents taking medications had been noncompliant during the month preceding the study interview. Noncompliance with prescribed medications was significantly associated with higher socioeconomic status (P < 0.01), greater number of prescribed medications (P < 0.01), and higher psychological stress (P < 0.05). There was no relationship between compliance and living arrangements, health, life satisfaction, number of illnesses, age, or sex.

Aged↗