Presentation Of Sensory Stimuli Research Articles

The Relationship between Trial-by-Trial Variability and Oscillations of Cortical Population Activity

Neural activity fluctuates over time, creating considerable variability across trials. This trial-by-trial neural variability is dramatically reduced (“quenched”) after the presentation of sensory stimuli. Likewise, the power of neural oscillations, primarily in the alpha-beta band, is also reduced after stimulus onset. Despite their similarity, these phenomena have so far been studied and discussed independently. We hypothesized that the two phenomena are tightly coupled in electrophysiological recordings of large cortical neural populations. To test this, we examined magnetoencephalography (MEG) recordings of healthy subjects viewing repeated presentations of a visual stimulus. The timing, amplitude, and spatial topography of variability-quenching and power-suppression were remarkably similar. Neural variability quenching was eliminated by excluding the alpha-beta band from the recordings, but not by excluding other frequency-bands. Moreover, individual magnitudes of alpha-beta band-power explained 86% of between-subject differences in variability quenching. An alternative mechanism that may generate variability quenching is increased phase alignment across trials. However, changes in inter-trial-phase-coherence (ITPC) exhibited distinct timing and no correlations with the magnitude of variability quenching in individual participants. These results reveal that neural variability quenching is tightly coupled with stimulus-induced changes in the power of alpha-beta band oscillations, associating two phenomena that have so far been studied in isolation.

Brain functional imaging in obese and diabetic patients.

Obesity and type 2 diabetes are associated with greater risk of brain damage. Over the last decade, functional imaging techniques (functional magnetic resonance imaging, fMRI, positron emission tomography, PET, electroencephalography, magnetoencephalography, near infrared spectroscopy) have been exploited to better characterize behavioral and cognitive processes, by addressing cerebral reactions to a variety of stimuli or tasks, including hormones and substrates (e.g., glucose, insulin, gut peptides), environmental cues (e.g., presentation of sensory stimuli), and cognitive tasks. Among these techniques, fMRI and PET are most commonly used, and this review focuses on results obtained with these techniques in relation to brain substrate metabolism, appetite control and food intake, and cognitive decline in obesity and type 2 diabetes. The available knowledge indicates that there are a series of cerebral abnormalities associating with, or preceding obesity and type 2 diabetes, including impaired substrate handling, insulin resistance, disruption of inter-organ cross-talk and of resting state networking. Some of these abnormalities are reversed by metabolic interventions, suggesting that they are partly a consequence rather than cause of disease. Therefore, causal implications and mechanisms remain to be determined.

Regulation of the Functional State of the Human Brain by Real-Time Frequency−Phase Synchronization of Sensory Stimuli with the EEG Rhythm

A method providing real-time digital EEG filtration in selected leads and assessment of the instantaneous amplitude and phase of the background rhythm to generate control signals for the presentation of sensory stimuli at specified phases of the dominant biorhythm is presented. Examples of phase-dependent rearrangements in EEG characteristics in humans detected using this method are given.

Increases in hippocampal and frontal cortical acetylcholine release associated with presentation of sensory stimuli

In vivo microdialysis was employed to monitor acetylcholine release in the hippocampus and frontal cortex of freely behaving rats. Four stimuli were presented on separate occasions in the course of a dialysis session to rats with microdialysis probes implanted in the hippocampus or frontal cortex. Visual, auditory, olfactory and tactile stimuli elicited a number of different responses such as exploratory and consummatory behaviours. Presentation of two of the stimuli (auditory and tactile) also produced periods of alert immobility (freezing). All of the stimuli increased acetylcholine release in both the hippocampus and cortex: in the hippocampus, this increase was statistically significant with all except the olfactory stimulus, whereas in the cortex all but the visual stimulus resulted in significant increases. In the hippocampus, there were no significant differences between the increases in acetylcholine release produced by the four stimuli. In contrast, in the cortex, there was significant variation between the magnitude of acetylcholine release produced by the different stimuli: acetylcholine release elicited by tactile stimulation was greater than that produced by the other stimuli. There was no significant variation in the duration of increases in acetylcholine release produced by the stimuli in either the hippocampus or cortex. These results provide evidence that acetylcholine release is associated with a variety of behavioural responses to stimuli designed to produce arousal, and point to a role for cortical and hippocampal cholinergic mechanisms in arousal or attention. Further, the results suggest that under some circumstances cortical and hippocampal acetylcholine release may be regulated differentially.

Effect of sensory input on the levels of enzymes involved in energy metabolism

Presentation of sensory stimuli of various modalities to rats immediately before their decapitation led to a significant increase in the level of succinate dehydrogenase in the hippocampus, the magnitude of the increase being dependent on the number of stimuli presented. In each individual case, this enzyme's activity was proportional to the amplitude of the population spike recorded in the hippocampus of the same rat. An inverse relationship was noted between the rate of plastic processes in the hippocampus upon rhythmic stimulation and succinate dehydrogenase activity.

Some electrophysiological characteristics of insular cortex efferents to the amygdaloid central nucleus in awake rabbits

Extracellular single unit recordings were obtained from insular cortex neurons that were activated antidromically from the amygdaloid central nucleus in conscious rabbits. Consistent with previous anatomical data, the majority of these neurons were located within the dorsal agranular insula. Ongoing activity in these neurons was infrequent, and was not altered during the presentation of sensory stimuli or during the expression of Pavlovian conditioned bradycardia. These results provide data relevant to the functional organization of forebrain areas thought to be involved in autonomic control.

The pharmacology of hippocampal theta cells: Evidence that the sensory processing correlate is cholinergic

The firing repertoires of theta cells in the CA1 and dentate layers of the hippocampal formation of the freely moving rabbit were analyzed during 3 behavioral conditions: (1) voluntary motor patterns, termed type 1 theta behaviors; (2) automatic motor patterns, termed type 2 LIA behaviors; (3) alert immobility with presentation of sensory stimuli, termed type 2 theta behavior. Cholinergic manipulations were shown to effect the firing repertoires of theta cells during the type 2 theta behavior condition (sensory processing) and not the other two behavioral conditions. A hypothesis of a sensorimotor processing function of the hippocampal formation is presented and discussed.

The relation of mutliple hippocampal theta cell discharge rates to slow wave theta frequency

Multiple theta cells in the dentate granule cell area of the hippocampal formation of the freely moving rabbit were analyzed during three behavioral conditions: (1) voluntary motor patterns, termed Type 1 theta behaviors; (2) automatic motor patterns, termed Type 2 LIA behaviors; (3) alert immobility with presentation of sensory stimuli, termed Type 2 theta behavior. Multiple theta cells showed a linear increase in discharge rates, with increasing frequency of slow wave theta, in both the Type 1 and Type 2 theta conditions. Although there was no mean overlap in discharge rates (from one frequency to the next highest frequency of slow wave theta), individual data points overlapped considerably in the middle ranges. Multiple theta cell discharge rates were significantly lower in the Type 2 theta condition compared to the Type 1 theta condition, even at identical slow wave theta frequencies. Multiple theta cells discharged in an irregular fashion during the Type 2 LIA behavior condition. The discharge pattern was characterized as on or off, the on pattern most commonly observed being asynchronous bursting.

Ontogeny of fascia dentata electrical activity and motor behavior in the dutch belted rabbit ( Oryctolagus cuniculus)

The development of dentate electroencephalographic (EEG) activity and motor behavior was studied in the neonatal rabbit. Using a combined longitudinal, cross-sectional design, neonatal rabbits were implanted with microelectrodes in the dentate region of the hippocampal formation. Recordings of electrical activity were made during the occurrence of spontaneous behaviors, during the presentation of sensory stimuli, and during the administration of eserine and atropine sulfate. Motor activities developed in parallel with the dentate EEG activity. Lowamplitude irregular activity accompanied the uncoordinated motor behaviors of rabbits 6 to 7 days of age. By 8 days, the EEG-behavioral correlation described by Vanderwolf became evident: certain types of movement were always accompanied by theta activity (type 1) whereas other types (including immobility) were accompanied by irregular activity. By 14 days of age, a second lower-frequency theta (type 2) developed. Type 2 theta occurred while the rabbit was immobile, spontaneously during the presentation of sensory stimulation (whistles, claps, and pure tones), and after the administration of the anticholinesterase drug, eserine. Administration of the anticholinergic drug, atropine sulfate, completely abolished type 2 theta activity. It was also demonstrated that in very young rabbits (between 8 and 15 days of age) atropine sulfate was nonselective in its effects, abolishing both movement-correlated theta (type 1) and immobility-related theta (type 2). Observations of REM sleep also demonstrated that theta activity first appeared at 8 days of age. Both types of theta showed a developmental increase in amplitude and frequency, attaining adult values by 23 days of age. Finally, the study supported previous findings that the dentate area of the hippocampal formation is one of the main generators of theta activity, and is capable of producing both types of theta.