Biomedical subjects

B Suresh Krishna

Publications and source records attributed to B Suresh Krishna.

4 recordsLinked to original sources

PubMed2006

Reaction times of manual responses to a visual stimulus at the goal of a planned memory-guided saccade in the monkey.

Monkeys demonstrate improved contrast sensitivity at the goal of a planned memory-guided saccade (Science 299:81-86, 2003). Such perceptual improvements have been ascribed to an endogenous attentional advantage induced by the saccade plan. Speeded reaction times have also been used as evidence for attention. We therefore asked whether the attentional advantage at the goal of a planned memory-guided saccade led to speeded manual reaction times following probes presented at the saccade goal in a simple detection task. We found that monkeys showed slower manual reaction times when the probe appeared at the memorized goal of the planned saccade when compared to manual reaction times following a probe that appeared opposite the saccade goal. Flashing a distractor at the saccade goal after target presentation appeared to slow reaction times further. Our data, combined with prior results, suggest that a spatially localized inhibition operates on the neural representation of the saccade goal. This inhibition may be closely related or identical to the processes underlying inhibition-of-return. We also found that if the same detection task was interleaved with a difficult perceptual discrimination task, manual reaction times became faster when the probe was at the saccade goal. We interpret these results as being an effect of task difficulty; the more difficult interleaved task may have engaged endogenous attentional resources more effectively, allowing it to override the inhibition at the saccade goal. We construct and discuss a simple working hypothesis for the relationship between the effects of prior attention on neural activity in salience maps and on performance in detection and discrimination tasks.

Animals↗

PubMed2006

Comment on "Auditory-nerve first-spike latency and auditory absolute threshold: a computer model" [J. Acoust. Soc. Am. 119, 406-417 (2006)].

A recent paper by Meddis [J. Acoust. Soc. Am. 119, 406-417 (2006)] shows that an existing model of the auditory nerve [Meddis and O'Mard, J. Acoust. Soc. Am. 117, 3787-3798 (2005)] is consistent with experimentally-measured first-spike latencies in the auditory nerve [Heil and Neubauer, J. Neurosci. 21, 7404-7415 (2001)]. The paper states that this consistency emerges because in the model, the calcium concentration inside the inner hair cell builds up over long periods of time (up to at least 200 ms) during tone presentation. It further states that integration over long time-scales happens despite the very short time constants (< 1 ms) used for the calcium dynamics. This letter demonstrates that these statements are incorrect. It is shown by simulation that calcium concentration inside the hair cell stage of the Meddis model rapidly reaches a steady state within a few milliseconds of a stimulus onset, exactly as expected from the short time-constant in the simple first-order differential equation used to model the calcium concentration. The success of the Meddis model in fitting experimental data actually confirms earlier results [Krishna, J. Comput. Neurosci. 13, 71-91 (2002a)] that show that the experimental data are a natural result of stochasticity in the synaptic events leading up to spike-generation in the auditory nerve; integration over long time scales is not necessary to model the experimental data.

Action Potentials↗

PubMed2004

A rapid and precise on-response in posterior parietal cortex.

The activity of neurons in the lateral intraparietal area (LIP) of the monkey predicts the monkey's allocation of spatial attention. We show here that despite being relatively high within the visual hierarchy, neurons in LIP have extremely short and precise visual latencies. Mean latency was 45.2 msec; the timing precision of the onset response was usually better than 4 msec. The majority of neurons had a pause in response after an initial burst, followed by more sustained visual activity. Previous attention allocation had no effect on either the latency or magnitude of the initial burst, but produced clear effects on the magnitude of the later sustained activity. Together, these data indicate that the initial burst in LIP visual response reflects an uncontaminated sensory signal. Information about stimulus onset is transmitted rapidly through the visual system to LIP; the on-response has a higher speed and temporal precision than realized previously. This information could be used to orient attention to novel objects in the visual environment rapidly and reliably.

Animals↗

PubMedDate not supplied

A unified mechanism for spontaneous-rate and first-spike timing in the auditory nerve.

Recent physiological experiments have provided detailed descriptions of the properties of first-spike latency and variability in auditory cortex and nerve in response to pure tones with different envelopes. The envelope-dependence of first-spike timing and precision in auditory cortical neurons appears to reflect properties established in the nerve. First-spike latency properties in individual auditory nerve fibers are strongly correlated with their spontaneous rate (SR). It is shown here that a minimal, plausible model of auditory transduction with two free parameters accurately reproduces the physiological data from the auditory nerve population. The model consists of a simple gain stage, a bandpass filter, a rectifying saturating non-linearity, and a lowpass filter in series. The output of the lowpass filter drives an inhomogeneous Poisson process. The shape of the non-linearity is determined by SR; in physiological terms, this shape depends upon the resting sensitivity of the synapse between the inner hair cell and the auditory nerve. An alternative model for SR generation, where SR is added to the stimulus-driven output of a fixed nonlinearity, fails to account for the data. The results provide a novel, comprehensive and physiologically-based explanation for the range of experimental results on the envelope-dependence of first-spike latency and precision, and its relationship with SR, in the auditory system.

Acoustic Stimulation↗