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At least 667 records · Page 37Linked to original sources
PubMed1983

On-line source-density computation with a minimum of electrodes.

An economical arrangement is described whereby the Laplacean of the scalp potential distribution delta2V/delta X2 + delta 2V/delta y2 can be approximately computed by analog methods, using a simple adaptation of the input stages of conventional EEG amplifiers. For maximum efficiency the method requires electrodes to be disposed in equilateral triangular arrays. This makes possible the computation of approximate source densities at 7 scalp locations for a total of only 13 electrodes.

Electrodes↗
PubMedDate not supplied

Probabilistic computation by neuromine networks.

In this paper, we address the question, can biologically feasible neural nets compute more than can be computed by deterministic polynomial time algorithms? Since we want to maintain a claim of plausibility and reasonableness we restrict ourselves to algorithmically easy to construct nets and we rule out infinite precision in parameters and in any analog parts of the computation. Our approach is to consider the recent advances in randomized algorithms and see if such randomized computations can be described by neural nets. We start with a pair of neurons and show that by connecting them with reciprocal inhibition and some tonic input, then the steady-state will be one neuron ON and one neuron OFF, but which neuron will be ON and which neuron will be OFF will be chosen at random (perhaps, it would be better to say that microscopic noise in the analog computation will be turned into a megascale random bit). We then show that we can build a small network that uses this random bit process to generate repeatedly random bits. This random bit generator can then be connected with a neural net representing the deterministic part of randomized algorithm. We, therefore, demonstrate that these neural nets can carry out probabilistic computation and thus be less limited than classical neural nets.

Algorithms↗
PubMed2001

Neurophysiologic testing in chronic pelvic pain syndrome: a pilot study.

OBJECTIVES: Studies of male chronic pelvic pain syndrome (CPPS) have generally centered on the pathologic features of the prostate rather than on the neurology of pain. Electrodiagnostic studies examine the integrity of somatosensory nerve pathways consisting of large, group A fibers. Heat sensation and visceral (autonomic) pain is mediated through small, unmyelinated C fibers, which can be tested cutaneously by thermal sensory analysis. We hypothesized that CPPS pain is mediated by these small C fibers. METHODS: All subjects and controls had no history of neurologic disease and had normal neurologic examinations. Phase I: 14 patients with CPPS underwent electrodiagnostic testing using pudendal somatosensory evoked potentials and bulbocavernosus reflex latency measurements. Phase II: 31 patients with CPPS and 14 controls underwent thermal sensory analysis testing on the perineum and anterior thigh using noxious heat stimuli. Subjects used a computer-generated visual analog scale to dynamically report their discomfort. The peak and slope of the computer-generated visual analog scale were analyzed. RESULTS: Phase I: two patients had delayed latency of the somatosensory evoked potentials, but additional evaluation with magnetic resonance imaging revealed no definable lesion. Phase II: with thermal sensory analysis, men with CPPS reported higher intensity pain at lower temperatures (P = 0.03). Men with CPPS also had higher peak computer-generated visual analog scale scores on perineal testing. No difference in thermal testing on the anterior thigh was found between the two groups. CONCLUSIONS: Large, myelinated somatic fibers do not play a significant role in the pathophysiology of CPPS. Patients with CPPS have an altered sensation of perineal pain elicited by heat, which may represent a C-fiber-mediated effect.

Chronic Disease↗
PubMed2001

The application of cross-point switch arrays as input selector switch devices for multi-channel electrophysiological experiments.

Integrated circuits (ICs) containing cross-point switch arrays were applied to create analog input selector switch devices for multi-channel electrophysiological experiments. The described analog input selector switch devices make it possible to connect to the main amplifier's inputs those microelectrode and preamplifier output wires that yield unit discharges of acceptable shape and amplitude, or yield other kind of acceptable electrophysiological signals (EEG, EP). This kind of selector allows to use higher number of preamplifier channels and to ignore the input channels without adequate signals or the channels with noisy inputs. No manual switching is required, as the work is done by computer controlled switches. The switch positions can be saved and reloaded at the next experimental session through an I/O port (e.g. the parallel port) of the computer.

Amplifiers, Electronic↗
PubMed1997

Storing analog data in a video record.

We have designed a simple device that will encode, in machine readable form, multiple analog data in a video record. The analog data is visible to the user within the video frame permitting visual correlation of these signals with activity observed in the image. By superimposition of both analog and video data sets, the two are tightly synchronized and remain so in all copies of the data. The analog data can be separated from the image following digitization by a frame grabber. The bandwidth for each of the five analog channels is approximately 5 kHz. The device, which is essentially an eight channel video multiplexor, includes a video channel, a field counter, an amplitude calibration signal and five analog data channels. The amplitude calibrator allows corrections for gain errors that are particularly prevalent when data is stored on video tape.

Calibration↗
PubMedDate not supplied

Silicon synaptic conductances.

We have developed compact analog integrated circuits that simulate two synaptic excitatory conductances. A four-transistor circuit captures the dynamics of an excitatory postsynaptic current caused by a real AMPA conductance. A six-transistor circuit simulates the effects of a real voltage-dependent NMDA conductance. The postsynaptic current dynamics are modeled by a current mirror integrator with adjustable gain. The voltage dependence of the silicon NMDA conductance is realized by a differential pair. We show the operation of these silicon synaptic conductances and their integration with the silicon neuron (Mahowald and Douglas, 1991).

Action Potentials↗
PubMed2005

Lateral somatotopic organization during imagined and prepared movements.

Motor imagery is a complex cognitive operation that requires memory retrieval, spatial attention, and possibly computations that are analogs of the physical movements being imagined. Likewise, motor preparation may or may not involve computations that are analogs of actual movements. To test whether motor imagery or motor preparation activate representations that are specific to the body part whose movement is imagined or prepared, participants performed, imagined, and prepared hand movements while undergoing functional MRI scanning. Actual hand movements activated components of the motor system including primary motor and somatosensory cortex, the supplementary motor area, the thalamus, and the cerebellum. All of these areas showed strong lateral organization, such that moving a given hand activated the contralateral cortex and ipsilateral cerebellum most strongly. During motor imagery and motor preparation, activity throughout the motor system was much reduced relative to overt movement. However, significant lateral organization was observed during both motor imagery and motor preparation in primary motor cortex, the supplementary motor area, and the thalamus. These results support the view that the subjective experience of imagined movement is accompanied by computations that are analogs of the physical movement that is imagined. They also suggest that in this regard motor imagery and motor preparation are similar.

Adult↗
PubMed1980

Simple kinematic gait measurements.

Simple kinematic gait measurement equipment was developed providing fast and inexpensive clinical gait analysis. Such a simple system can be used as a stand-alone clinical gait analyser, or as an accessory for measurements whose results are not sufficiently weighted statistically, such as TV, Selspot, force plate. Time, distance and velocity parameters are included in the clinical gait analysis. Time parameters (step and stride time, swing and stance phase) are measured via easily attachable foot-switches. Analog and digital versions were developed to analyse distance (stride and step length) and velocity (instantaneous velocity of centre of gravity) parameters. With the analog device the velocity is measured by tachometer and distance by potentiometer, while using digital methods, both parameters can be obtained from an optical transducer.

Biomedical Engineering↗
PubMed1993

Inhibition of estrogen stimulated mitogenesis by 3-phenylacetylamino-2,6-piperidinedione and its para-hydroxy analog.

3-Phenylactetylamino-2,6-piperidinedione (A10) inhibited estradiol stimulated cell growth in the MCF-7 (E3) human breast tumor cell line in vivo and in vitro. While high concentrations of A10 were needed to inhibit cell proliferation (IC50 = 3 x 10(-3) M in vitro), the compound demonstrated little toxicity. The effect appeared specific since a hydrolysis product of A10, phenylacetylglutamine, demonstrated no growth inhibitory activity at similar concentrations in MCF-7 (E3) cells in vitro. A computer designed analog, p-hydroxy A10, was more potent than A10 in inhibiting activity in MCF-7 (E3) cells in vitro. The IC50 for p-hydroxy A10 was 7 x 10(-6) M which was comparable to that of the antiestrogen, tamoxifen (IC50 1 x 10(-7) M). All three compounds caused a decline in estrogen receptor levels in a dose-dependent fashion. A10 also inhibited estradiol induction of progesterone receptors. Examination of protein kinase activity following an acute exposure to a 10(-11) M growth stimulatory dose of estradiol revealed a 168% increase in protein kinase activity over that of untreated control cells. A10 in a dose-responsive fashion inhibited the estradiol stimulated increase in protein kinase activity. The protein kinase activity was also inhibited by p-hydroxy A10. These activities of A10 and p-hydroxy A10 coupled with the low toxicity and novelty of the basic A10 structure provide an exciting possibility of developing a new class of clinically useful antineoplastic drugs with minimal side effects.

Animals↗
PubMed1980

Effects of analog and digital filtering on brain stem auditory evoked potentials.

Most investigators of the brains stem auditory evoked potentials utilize analog filters to reduce the noise content of the averaged signals, but different investigators use different filter bandwidths. Data presented in this note compare the effects of different upper and lower cutoff frequencies for both analog and zero-phase shift digital filters. Effects on response wave form and on measured values of amplitude and latency of wave V are considered. It is concluded that, for given cutoff frequencies, analog filtering causes more distortion of the response than digital filtering, due primarily to phase distortion introduced by the analog filter. It is likely that differences in filter cutoff frequencies, especially lower cutoff frequencies, are a significant source of variability in results reported by different investigators.

Auditory Perception↗
PubMed1990

Computer simulation of ciprofloxacin pharmacokinetics in patients on CAPD.

Continuous ambulatory peritoneal dialysis (CAPD) has become an accepted alternative to chronic hemodialysis in the treatment of end-stage renal disease. The method utilizes the diffusion of drugs from the blood through the peritoneal membrane to the peritoneal cavity if administered intravenously (IV) and perorally (PO) and in the opposite direction if applied intraperitoneally (IP). The present work uses an open, two-compartment pharmacokinetic model reversibly linked with the compartment representing the peritoneal cavity and an analog-hybrid computer to simulate drug levels in sampled and unsampled compartments under conditions of various routes of administration (IV, IP and sequential IV, IP and PO) and different clinical status (presence and absence of peritonitis). The drug chosen for simulation was ciprofloxacin (CIP), a new synthetic antibacterial agent of the 4-quinolone group. Eight patients were included in the study, and CIP concentrations in plasma and dialysate were obtained by HPLC analysis to assess the reliability of the model and the efficiency of the sequential dosing scheme. CIP plasma and dialysate levels were adequate for the majority of microbes causing CAPD peritonitis. The proposed regimen was efficient in 85% of cases.

Administration, Oral↗
PubMed1976

Electrical off response of cat esophageal smooth muscle: an analog simulation.

This investigation was performed to define characteristics and to design an electrical model of the slow membrane depolarization, or "electrical off response," that follows stimulation of cat circular esophageal smooth muscle. The electrical off response showed the following characteristics: 1) the response was preceded by hyperpolarization of the muscle membrane; 2) the amplitude of the off-response depolarization increased directly with increasing amplitude of the preceding hyperpolarization; 3) the membrane potential showed varying degrees of oscillation around the resting point; 4) the oscillation period was constant (4-5 s) and was double the time from the point of maximum hyperpolarization to the peak of the electrical off response. These characteristics suggested that the electrical off response could be represented by a linear second-order differential equation with variable damping, and an analog simulation was constructed. By varying the damping ratio and/or the natural frequency of the analog model, the characteristics of the electrical off response of esophageal muscle could be reproduced. The model provides a means to explore the behavior of esophageal smooth muscle contraction under normal and pathological conditions.

Animals↗