Search PubMed⌕ Search

Biomedical subjects

P R Kennedy

Publications and source records attributed to P R Kennedy.

At least 19 recordsLinked to original sources
PubMed2003

A decision tree for brain-computer interface devices.

This paper is a first attempt to present a "decision tree" to assist in choosing a brain-computer interface device for patients who are nearly or completely "locked-in" (cognitively intact but unable to move or communicate.) The first step is to assess any remaining function. There are six inflexion points in the decision-making process. These depend on the functional status of the patient: 1) some residual movement; 2) no movement, but some residual electromyographic (EMG) activity; 3) fully locked-in with no EMG activity or movements but with conjugate eye movements; 4) same as 3 but with disconjugate eye movements; 5) same as 4 but with inadequate assistance from the available EEG-based systems; 6) same as 5 and accepting of an invasive system.

Algorithms↗
PubMed2001

Simplified serum- and steroid-free culture conditions for high-throughput viability analysis of primary cultures of cerebellar granule neurons.

A serum- and steroid-free primary culture system was developed for the maintenance and automated analysis of cerebellar granule cell viability. Conventional poly-lysine coated 96-well tissue culture plates serve as a platform for growth, experimental manipulation and subsequent automated analysis of these primary cultured neurons. Cerebellar granule neurons were seeded at densities ranging from 2 x 10(4) to 1.25 x 10(6) cells/cm(2) and maintained in serum- and steroid-free culture conditions for 7 days. Viability was subsequently determined by the reduction of [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS), and the degree of cell death occurring over that period was determined by the release of lactate dehydrogenase (LDH). At appropriate cell densities, the results of the MTS reduction and LDH release assays were directly proportional to the initial number of cerebellar granule cells plated. Those results indicate that an initial cell density of 0.5 - 1.0 x 10(5) cells per well (0.32 cm(2)) was appropriate for simultaneous analysis with the MTS reduction and LDH release assays. Both assays were then used to demonstrate the utility of this model system for analysis of tert-butyl-hydroperoxide and hydrogen peroxide induced oxidative stress. Additionally, the MTS reduction assay was used to demonstrate that the NMDA-receptor selective antagonist MK-801 was neuroprotective against glutamate-mediated excitotoxicity. This study defines a powerful and flexible primary culture system for cerebellar neurons that is useful for high-throughput analysis of factors that influence neuronal viability.

Animals↗
PubMed2000

Direct control of a computer from the human central nervous system.

We describe an invasive alternative to externally applied brain-computer interface (BCI) devices. This system requires implantation of a special electrode into the outer layers of the human neocortex. The recorded signals are transmitted to a nearby receiver and processed to drive a cursor on a computer monitor in front of the patient. Our present patient has learned to control the cursor for the production of synthetic speech and typing.

Biofeedback, Psychology↗
PubMed1998

Restoration of neural output from a paralyzed patient by a direct brain connection.

Patients with severe paralysis of limbs, face and vocal apparatus may be intelligent and aware and yet, tragically, unable to communicate. We describe a communication link for such a 'locked-in' patient with amyotrophic lateral sclerosis. We recorded action potentials in her brain over several months by means of an electrode that induces growth of myelinated fibers into its recording tip. She was able to control the neural signals in an on/off fashion. This result is an important step towards providing such patients with direct control of their environment by interfacing with a computer. Additionally, it indicates that restoration of paralyzed muscles may be possible by using the signals to control muscle stimulators.

Action Potentials↗
PubMed1997

Activity of single action potentials in monkey motor cortex during long-term task learning.

Studies using continuous recording of neural activity during long-term learning are now possible with an implanted neurotrophic electrode. During recording of individual cortical action potentials in monkeys performing a reach and grasp task, we were able to follow the gradual change in firing of several action potentials as the task was learned. Control experiments suggest that the neurons involved in the learning were initially silent.

Action Potentials↗
PubMed1997

Retrospinal tract.

Explore the source record for details and available documents.

Efferent Pathways↗
PubMed1992

The cone electrode: ultrastructural studies following long-term recording in rat and monkey cortex.

The achievement of long-term recording of neural signals from the central nervous system has potential clinical and investigative application. To facilitate long-term recording, a novel cone electrode composed of an insulated gold wire within a hollow glass cone had been developed. Cone electrodes containing sciatic nerve or neurotrophic medium were implanted into cerebral cortex in rats and monkeys. Electrophysiologic recordings had been previously obtained from cone tissue for as long as 15 months following implantation and this tissue contained silver-positive processes. We now extend these observations to characterize the fine structural features of the tissue within these long-term implants. Electron microscopy revealed central myelinated axons, dendrites, synaptic profiles, blood vessels, and glia; peripheral nerve was not found in the cones in which sciatic nerve had been placed. These observations further suggest ingrowth of cortical neurites and elements into the hollow glass tip of the cone and support the feasibility of long-term recording using this electrode.

Animals↗
PubMed1992

Behavioral correlates of action potentials recorded chronically inside the Cone Electrode.

Long-term recording of stable action potentials with a new electrode configuration has been achieved for up to 15 months in monkeys. Action potentials are separated from the continuous multi-unit recordings made between two wires inside a glass open ended cone implanted in the motor cortex. Neural tissue is induced to grow into the glass cone by autologous sciatic nerve placed inside prior to implantation. Data presented here show that behavioral correlates of neural activity are related to flexion and extension movements of the contralateral hand and digits. These data suggest that this electrode can be used in both basic and applied studies.

Action Potentials↗
PubMed1992

Altered cellular calcium regulation and hepatic glucose production during hemorrhagic shock.

The relationship between intracellular Ca2+ and glucose production in the liver during early and late states of hemorrhagic shock was studied. Rats were anesthetized with intraperitoneal sodium pentobarbital and both femoral arteries and one femoral vein were cannulated. Rats were divided into two groups. One group was subjected to hemorrhagic shock by rapid withdrawal of blood to a mean arterial pressure of 40 mm Hg and maintained in shock for either 30 or 150 min. Rats in the control group were observed for the same time period. Hepatic glucose production was evaluated in both groups by a nonrecirculating liver perfusion model with and without lactate as a substrate. Intracellular free Ca2+ in hepatocytes was measured using the Ca2+ selective indicator Fura-2, under basal and epinephrine-stimulated conditions. Hyperglycemia and hyperlacticacidemia were observed in vivo at 30 min of hemorrhagic shock, whereas hypoglycemia and hyperlacticacidemia were observed at 150 min of shock. Hepatic glucose production in isolated perfused livers was significantly depressed at 30 min in animals subjected to shock (P less than 0.05). Lactate-induced glucose production was significantly attenuated at 30 and 150 min (P less than 0.05). Basal Ca2+, in isolated hepatocytes, at 30 and 150 min of hemorrhagic shock was significantly (P less than 0.05) higher than in controls. The hemorrhagic shock rat hepatocytes failed to evaluate intracellular free Ca2+ upon stimulation with 10(-5) M epinephrine. These results demonstrate that hemorrhagic shock is associated with an increase in hepatocyte intracellular Ca2+ concentration along with attenuation of hormone-mediated mobilization of calcium and substrate specific stimulation of hepatic glucose production.

Animals↗
PubMed1991

T3 preserves respiratory function in sepsis.

Sepsis produces profound hypothyroidism. This hypothyroid state is associated with altered lung metabolism and structural integrity. We studied the respiratory function of rats during sepsis-induced hypothyroidism with or without T3 treatment. Forty-four male Holtzman rats underwent cecal ligation and puncture (CLP). Treatment was administered at six hours after surgery consisting of intraperitoneal injection of T3 (15 micrograms/kg, n = 19) or saline (n = 25). At 20 hours (Group A) or 30 hours (Group B) following CLP, respiratory drive was assessed by serial occlusion pressure technique (P0.1). The rats were killed and static elastance determined by serial air inflation to 10 cc. The lungs were excised for weight determination. The P0.1 values were significantly greater in T3-treated animals over controls in Group A (9.3 +/- 0.7 vs. 6.6 +/- 2.2, p less than 0.05 by t test); elastance was significantly improved by T3 treatment in Group B (p less than 0.05 by two-way ANOVA). Lung weight, pH, pO2, pCO2, respiratory rate (RR), and mortality were not significantly different between groups. Control animals were hypothyroid by 20 hours after CLP (T3 less than 12.5 ng/dL) whereas T3-treated animals were euthyroid (T3 = 145 +/- 43 ng/dL). Pulmonary dysfunction frequently accompanies sepsis; the euthyroid state appears protective. We found a significantly improved respiratory drive in septic animals with T3 treatment. Lung elastance was similarly improved in late sepsis with T3 treatment. The data suggest that T3 treatment preserves respiratory function in septic rats as evidenced by respiratory drive and compliance.

Airway Resistance↗
PubMed1991

Autologous fibrin gel: bactericidal properties in contaminated hepatic injury.

Fibrin glue is an effective hemostatic agent in a variety of clinical situations; its utility is limited by potential transmission of viral infection. We studied the bactericidal properties of fibrin gel (FG) in a murine contaminated hepatic injury model and in vitro by agar plate culture method. Intra-abdominal abscess formation and adhesion rate were assessed following controlled liver injury in association with abdominal contamination with 10(7) Bacteroides fragilis and hepatorrhaphy (H, n = 15) or FG (n = 12). Animals treated by hepatorrhaphy had a significantly greater intra-abdominal abscess rate (15/15 vs. 4/12, p less than 0.05) and adhesion rate (14/15 vs. 6/12, p less than 0.05) than animals treated with FG. Fibrin gel is bactericidal to Bacteroides fragilis, Enterobacter faecium, Escherichia coli, and Staphylococcus aureus but has no effect against Klebsiella pneumoniae or Pseudomonas aeruginosa; the plasma component appears active. Fibrin gel demonstrates significant improvement in adhesion formation and intra-abdominal abscess rate when compared with suture hepatorrhaphy. Fibrin gel appears protective in contaminated hepatic injury.

Abscess↗
PubMed1990

Corticospinal, rubrospinal and rubro-olivary projections: a unifying hypothesis.

There has been a dispute about the corticospinal and rubrospinal tracts for about 100 years. Both are descending motor pathways and have remarkably similar functional properties. It has been proposed previously that each system is primarily active in different movement contexts. The corticospinal tract is most involved when a new movements is being learnt, while the rubrospinal tract is preferentially active when automated movements are being executed. However, what structure decides which system should be in use? In this article Philip Kennedy discusses the evidence that the rubro-olivary tract switches between the two systems depending on the context of the movement.

Animals↗
PubMed1989

The cone electrode: a long-term electrode that records from neurites grown onto its recording surface.

A novel long-term recording electrode combines neural regeneration with a standard wire recording technique. The electrode consists of an insulated gold wire fixed inside a hollow glass cone. A piece of sciatic nerve is placed in the glass cone before implantation in cortex of rat. Cortical neurites grow into the sciatic nerve in the cone from surrounding neurons and their electrical activity is recorded via the wire (or wires) in the cone. This activity increases in amplitude over the first few weeks after implantation and remains stable until termination of the experiment many months later. Activity of both single and multi units has been recorded. The cone electrode opens unique opportunities for studies of neurite growth in vivo, for plasticity studies on a captive set of neurites, for studying the neural correlates of behavior and motor learning, and for accessing the central nervous systems of patients with severe paralysing and communicative disorders.

Animals↗
PubMed1987

Parametric relationships of individual digit movements to neuronal discharges in primate magnocellular red nucleus.

Single units were recorded in the magnocellular red nucleus (RNm) while digit movements were monitored in a monkey performing on an individual digit device. The monkey was trained to press switches for water reward while optical systems of infrared emitters and diodes were taped to thumb, index, middle and ring digits for monitoring movements. Of 53 neurons recorded while operating the individual digit device, 9 showed statistically significant parametric relationships with movement velocity and duration. Onset of activity preceded movement by an average of 90 +/- 26 ms. This result suggests that a small group of neurons in the forelimb area of RNm in the monkey is parametrically related to individual digit movements, even though the majority of neurons are related to grouped movements of the hand and digits as previously reported.

Animals↗
PubMed1987

Light labeling of red nucleus neurons following an injection of peroxidase-conjugated wheat germ agglutinin into the inferior olivary nucleus of the rat.

Since the rubro-olivary projection has not been demonstrated in the rat, unlike the monkey and cat (refs. in text). HRP or highly-concentrated wheat germ agglutinin-horseradish peroxidase (WGA-HRP) was injected into the inferior olivary nucleus using a ventral approach. After processing with a modified technique, sections were examined under high power. Three rats injected with WGA-HRP showed labelling in the red nucleus. In one of those rats with a well-confined injection, 583 neurons contained grains of HRP reaction product consistent with light retrograde labeling. This observation lends support to the existence of a rubro-olivary projection in the rat.

Animals↗
PubMed1987

The compensatory role of the parvocellular division of the red nucleus in operantly conditioned rats.

To assess the role of the parvocellular division of the red nucleus in motor control, rats were operantly conditioned to walk on a rotating bar and their red nuclei were lesioned with the fiber sparing agent, quinolinic acid. Since both parvocellular and magnocellular divisions of the red nucleus overlap in the rat, they both became involved in this lesion. To differentiate between them, two paradigms were used. (1) Prior to the lesion, the magnocellular division was dysfunctioned by transecting its spinal output, namely, the rubrospinal tract, in the dorso-lateral funiculus (DLF) of the spinal cord. After compensation for this transection had occurred in a few days, the red nucleus was lesioned with quinolinic acid. Rats again compensated rapidly, suggesting that the remaining red nuclear outflow systems, such as the rubro-olivary tract, play no detectable role in the control of on-going movements. (2) In the second paradigm, the red nucleus was lesioned without a preceding DLF transection. This lesion involved both the rubro-bulbar and rubro-spinal projections. Rats did not compensate, or did so very slowly. For compensation to occur, therefore, rubro-bulbar projections need to be intact. This suggests that such projections, that include the rubro-olivary tract, play a role in the compensation for DLF transections.

Animals↗