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PubMed1986

The influence of alcohol on the outcome of automated static perimetry.

It is well known that perimetric findings fluctuate within a single examination. There is additional fluctuation between perimetric examinations. The cause of this fluctuation is not yet fully understood, but such things as changes in attention, patient cooperation, or drugs have been discussed. To study such possible factors, we carried out perimetry on subjects who had consumed alcohol and who had not. The results indicate that alcohol, at a blood concentration of approximately 0.08%, barely influences the results of static automated perimetry. Differential light sensitivity remained unchanged by alcohol at all eccentricities tested. A decrease in the ability to cooperate was manifested by a significant higher score of false-positives in catch trials. There was also a tendency toward an increase in false-negative responses in catch trials, an increase in the number of stimuli presentations required, and higher short-term fluctuation. Lack of the influence of alcohol on the differential light threshold does not necessarily mean that alcohol has no influence on visual function. It indicates, however, that differential light sensitivity, as measured with the automated perimeter Octopus, is not influenced by moderate alcohol ingestion.

Adolescent↗
PubMed2002

Neurons evaluate both the amplitude and the meaning of signals.

The neuronal threshold, which can be determined by the level of depolarization immediately prior to spike generation, is different for responses to conditioned and discriminated stimuli after conditioning. However, it is impossible to determine excitability within a response to stimuli that failed to generate a spike. In the present study we examined the role of the AP threshold of two related Helix defensive neurons in the initiation of an AP during elaboration of the neuronal analog of a classical conditional reflex. These neurons fire in a synchronous manner though spikes sometimes are not generated simultaneously. We compared the change in spike threshold within the responses with other parameters of intracellular activity that also affect the neuronal response, but which can be measured without an analysis of the spike waveform (spike latency, slope of excitatory postsynaptic potentials, etc.). We found that the change in slope is not the reason for the change in the threshold during pairing. The thresholds within conditioned and discriminated responses affected spike generation and their values correlated with the spike presence or absence in related neurons. The excitability changed transiently within the responses, since these alterations were selective for the conditioned and discriminated stimuli and applied primarily to the first spike of the response. The firing threshold seems to be a dynamic property of excitable membrane. Neurons appear to evaluate the significance of the input signal, transiently change their own excitability and only after that compare the magnitude of this signal and threshold.

Action Potentials↗
PubMed2005

Correspondence between the location of evoked potential generators and sites of maximal sensitivity to stimulation.

The potential recorded by a set of electrodes as an action potential traverses a small axonal segment is proportional to the transmembrane potential produced during stimulation of that axon segment by the same set of recording electrodes, under certain circumstances. First, the membrane must have a constant thickness which is so small that the difference between the surface area of the inner and outer surfaces is minimal. Second, all media must be linear. Third, there must be a monotonically increasing relation between the mean transmembrane potential induced by a stimulus and the maximum transmembrane potential. Fourth, as each axon segment depolarizes, the transmembrane current and change in membrane potential during this time are same. This principle remains true for magnetic stimulation and recording as long as currents generated at the boundaries between regions of differing conductivity outside the axon contribute minimally to the field at the axon. This allows the identification of the point at which an action potential generates a maximal extracellular potential as the point that is stimulated with the lowest threshold.

Action Potentials↗
PubMed2002

Thresholding reflux episodes in impedance measurements using a neuro-fuzzy system.

Multiple intraluminal impedance measurements (MII) provides impedance signals which reflect the changes in the electrical conductivity inside the gastrointestinal tract (GIT). To determine a reflux episode from MII signals, wavelet transform is used to detect the edges of the impedance, then thresholding impedance at certain level. A predictor for the value of the threshold is constructed by training a fuzzy system using a number of features. During training process the predictor clusters the features into classes of similar feature values. The trained system is used to predict the threshold applied on the distal channel. Subsequently, a combination of wavelet transform and fuzzy logic is used to classify the episodes. In this paper we present the results of one stage of the system that predicts the threshold applied on the impedance value.

Differential Threshold↗
PubMed1987

Can tinnitus mask hearing? A comparison between subjective audiometric and objective electrophysiological thresholds in patients with tinnitus.

Very little has been written in the literature about the masking effect of tinnitus on hearing. This possibility arose from the clinical observations of hearing fluctuating with the intensity of tinnitus. To explore this hypothesis, a group of 19 patients suffering from hearing loss and tinnitus underwent a complete audiological evaluation and their audiometric and ABR thresholds were compared. Two other groups who were examined in the same manner, served as control groups. The first group consisted of 19 age- and sex-matched subjects with relatively normal hearing and no tinnitus. The second control group was composed of 8 patients suffering from sensorineural hearing loss without tinnitus. The differences between the subjective and ABR thresholds within each group and between the groups were statistically analyzed. The objective thresholds in the tinnitus group were found to be lower than the subjective thresholds.

Adult↗