Spike Potential Activity Research Articles

Encoding of long-term associations through neural unitization in the human medial temporal lobe

Besides decades of research showing the role of the medial temporal lobe (MTL) in memory and the encoding of associations, the neural substrates underlying these functions remain unknown. We identified single neurons in the human MTL that responded to multiple and, in most cases, associated stimuli. We observed that most of these neurons exhibit no differences in their spike and local field potential (LFP) activity associated with the individual response-eliciting stimuli. In addition, LFP responses in the theta band preceded single neuron responses by ~70 ms, with the single trial phase providing fine tuning of the spike response onset. We postulate that the finding of similar neuronal responses to associated items provides a simple and flexible way of encoding memories in the human MTL, increasing the effective capacity for memory storage and successful retrieval.

Brain activity mapping at multiple scales with silicon microprobes containing 1,024 electrodes.

The coordinated activity of neural ensembles across multiple interconnected regions has been challenging to study in the mammalian brain with cellular resolution using conventional recording tools. For instance, neural systems regulating learned behaviors often encompass multiple distinct structures that span the brain. To address this challenge we developed a three-dimensional (3D) silicon microprobe capable of simultaneously measuring extracellular spike and local field potential activity from 1,024 electrodes. The microprobe geometry can be precisely configured during assembly to target virtually any combination of four spatially distinct neuroanatomical planes. Here we report on the operation of such a device built for high-throughput monitoring of neural signals in the orbitofrontal cortex and several nuclei in the basal ganglia. We perform analysis on systems-level dynamics and correlations during periods of conditioned behavioral responding and rest, demonstrating the technology's ability to reveal functional organization at multiple scales in parallel in the mouse brain.

Whisker barrel cortex delta oscillations and gamma power in the awake mouse are linked to respiration

Current evidence suggests that delta oscillations (0.5–4 Hz) in the brain are generated by intrinsic network mechanisms involving cortical and thalamic circuits. Here we report that delta band oscillation in spike and local field potential (LFP) activity in the whisker barrel cortex of awake mice is phase locked to respiration. Furthermore, LFP oscillations in the gamma frequency band (30–80 Hz) are amplitude modulated in phase with the respiratory rhythm. Removal of the olfactory bulb eliminates respiration-locked delta oscillations and delta-gamma phase-amplitude coupling. Our findings thus suggest respiration-locked olfactory bulb activity as a main driving force behind delta oscillations and gamma power modulation in the whisker barrel cortex in the awake state.

Differential Entrainment and Learning-Related Dynamics of Spike and Local Field Potential Activity in the Sensorimotor and Associative Striatum

Parallel cortico-basal ganglia loops are thought to have distinct but interacting functions in motor learning and habit formation. In rats, the striatal projection neuron populations (MSNs) in the dorsolateral and dorsomedial striatum, respectively corresponding to sensorimotor and associative regions of the striatum, exhibit contrasting dynamics as rats acquire T-maze tasks (Thorn et al., 2010). Here, we asked whether these patterns could be related to the activity of local interneuron populations in the striatum and to the local field potential activity recorded simultaneously in the corresponding regions. We found that dorsolateral and dorsomedial striatal fast-spiking interneurons exhibited task-specific and training-related dynamics consistent with those of corresponding MSN populations. Moreover, both MSNs and interneuron populations in both regions became entrained to theta-band (5-12 Hz) frequencies during task acquisition. However, the predominant entrainment frequencies were different for the sensorimotor and associative zones. Dorsolateral striatal neurons became entrained mid-task to oscillations centered ∼ 5 Hz, whereas simultaneously recorded neurons in the dorsomedial region became entrained to higher frequency (∼ 10 Hz) rhythms. These region-specific patterns of entrainment evolved dynamically with the development of region-specific patterns of interneuron and MSN activity, indicating that, with learning, these two striatal regions can develop different frequency-modulated circuit activities in parallel. We suggest that such differential entrainment of sensorimotor and associative neuronal populations, acquired through learning, could be critical for coordinating information flow throughout each trans-striatal network while simultaneously enabling nearby components of the separate networks to operate independently.

Comparison of LFP-Based and Spike-Based Spectro-Temporal Receptive Fields and Cross-Correlation in Cat Primary Auditory Cortex

Multi-electrode array recordings of spike and local field potential (LFP) activity were made from primary auditory cortex of 12 normal hearing, ketamine-anesthetized cats. We evaluated 259 spectro-temporal receptive fields (STRFs) and 492 frequency-tuning curves (FTCs) based on LFPs and spikes simultaneously recorded on the same electrode. We compared their characteristic frequency (CF) gradients and their cross-correlation distances. The CF gradient for spike-based FTCs was about twice that for 2–40 Hz-filtered LFP-based FTCs, indicating greatly reduced frequency selectivity for LFPs. We also present comparisons for LFPs band-pass filtered between 4–8 Hz, 8–16 Hz and 16–40 Hz, with spike-based STRFs, on the basis of their marginal frequency distributions. We find on average a significantly larger correlation between the spike based marginal frequency distributions and those based on the 16–40 Hz filtered LFP, compared to those based on the 4–8 Hz, 8–16 Hz and 2–40 Hz filtered LFP. This suggests greater frequency specificity for the 16–40 Hz LFPs compared to those of lower frequency content. For spontaneous LFP and spike activity we evaluated 1373 pair correlations for pairs with >200 spikes in 900 s per electrode. Peak correlation-coefficient space constants were similar for the 2–40 Hz filtered LFP (5.5 mm) and the 16–40 Hz LFP (7.4 mm), whereas for spike-pair correlations it was about half that, at 3.2 mm. Comparing spike-pairs with 2–40 Hz (and 16–40 Hz) LFP-pair correlations showed that about 16% (9%) of the variance in the spike-pair correlations could be explained from LFP-pair correlations recorded on the same electrodes within the same electrode array. This larger correlation distance combined with the reduced CF gradient and much broader frequency selectivity suggests that LFPs are not a substitute for spike activity in primary auditory cortex.

Free choice activates a decision circuit between frontal and parietal cortex

We often face alternatives that we are free to choose between. Planning movements to select an alternative involves several areas in frontal and parietal cortex that are anatomically connected into long-range circuits. These areas must coordinate their activity to select a common movement goal, but how neural circuits make decisions remains poorly understood. Here we simultaneously record from the dorsal premotor area (PMd) in frontal cortex and the parietal reach region (PRR) in parietal cortex to investigate neural circuit mechanisms for decision making. We find that correlations in spike and local field potential (LFP) activity between these areas are greater when monkeys are freely making choices than when they are following instructions. We propose that a decision circuit featuring a sub-population of cells in frontal and parietal cortex may exchange information to coordinate activity between these areas. Cells participating in this decision circuit may influence movement choices by providing a common bias to the selection of movement goals.

Time-varying covariance of neural activities recorded in striatum and frontal cortex as monkeys perform sequential-saccade tasks

Cortico-basal ganglia circuits are key parts of the brain's habit system, but little is yet known about how these forebrain pathways function as ingrained habits are performed. We simultaneously recorded spike and local field potential (LFP) activity from regions of the frontal cortex and basal ganglia implicated in visuo-oculomotor control as highly trained macaque monkeys performed sequences of visually guided saccades. The tasks were repetitive, required no new learning, and could be performed nearly automatically. Our findings demonstrate striking differences between the relative timing of striatal and cortical activity during performance of the tasks. At the onset of the visual cues, LFPs in the prefrontal cortex and the oculomotor zone of the striatum showed near-synchronous activation. During the period of sequential-saccade performance, however, peak LFP activity occurred 100-300 msec later in the striatum than in the prefrontal cortex. Peak prefrontal activity tended to be peri-saccadic, whereas peak striatal activity tended to be post-saccadic. This temporal offset was also apparent in pairs of simultaneously recorded prefrontal and striatal neurons. In triple-site recordings, the LFP activity recorded in the supplementary eye field shared temporal characteristics of both the prefrontal and the striatal patterns. The near simultaneity of prefrontal and striatal peak responses at cue onsets, but temporal lag of striatal activity in the movement periods, suggests that the striatum may integrate corollary discharge or confirmatory response signals during sequential task performance. These timing relationships may be signatures of the normal functioning of striatal and frontal cortex during repetitive performance of learned behaviors.

Oscillatory neuronal synchronization in primary visual cortex as a correlate of stimulus selection.

Spike and local field potential activity were recorded simultaneously from multiple sites in primary visual cortex of strabismic cats, while monocular stimulation alternated with dichoptic stimulation, inducing interocular rivalry. During interocular rivalry, there is competition between the two nonfusible stimuli presented to the two eyes, and only one stimulus is selected at any time. We biased this competition in three different ways: (1) we exploited the condition that in strabismic cats there is often one dominant eye that is selected for most of the time. (2) We presented the two stimuli with a temporal offset, which biases competition in favor of the newly appearing stimulus. (3) We presented the two stimuli with highly different contrasts, which biases competition in favor of the stimulus with higher contrast. Whenever competition was biased in favor of the stimulus activating the recorded neurons, gamma-frequency synchronization of the respective responses was enhanced, and vice versa. Firing rates showed some differences between stimulation conditions. However, when present, these changes were inversely related to a competitive advantage of the respective stimulus. We hypothesize that enhanced gamma-frequency synchronization in primary visual cortex is a correlate of stimulus selection. Synchronization is likely to be translated into firing rate changes at later processing stages.

Oscillatory Neuronal Synchronization in Primary Visual Cortex as a Correlate of Stimulus Selection

Spike and local field potential activity were recorded simultaneously from multiple sites in primary visual cortex of strabismic cats, while monocular stimulation alternated with dichoptic stimulation, inducing interocular rivalry. During interocular rivalry, there is competition between the two nonfusible stimuli presented to the two eyes, and only one stimulus is selected at any time. We biased this competition in three different ways: (1) we exploited the condition that in strabismic cats there is often one dominant eye that is selected for most of the time. (2) We presented the two stimuli with a temporal offset, which biases competition in favor of the newly appearing stimulus. (3) We presented the two stimuli with highly different contrasts, which biases competition in favor of the stimulus with higher contrast. Whenever competition was biased in favor of the stimulus activating the recorded neurons, gamma-frequency synchronization of the respective responses was enhanced, and vice versa. Firing rates showed some differences between stimulation conditions. However, when present, these changes were inversely related to a competitive advantage of the respective stimulus. We hypothesize that enhanced gamma-frequency synchronization in primary visual cortex is a correlate of stimulus selection. Synchronization is likely to be translated into firing rate changes at later processing stages.

Intestinal myoelectric alterations in rats chronically infected with the tapeworm Hymenolepis diminuta

This study determined that intestinal myoelectric activity was profoundly altered during a strictly luminal, chronic, tapeworm infection. Chronically implanted bipolar electrodes were attached to five sites on the serosal surface of the rat small intestine. One was placed on the duodenum, three on the jejunum, and the fifth on the ileum. Electromyographic recording in nonfasted unanesthetized animals was begun at day 5 postsurgery. All electromyographic recordings were analyzed for slow wave (SW) frequency, phase III frequency, duration of phase III, and percentage of SW with spike potentials. Three initial control recordings prior to infection confirmed the presence of normal interdigestive motility characterized by the three phases (I, II, III) of the migrating myoelectric complex (MMC). Two nonpropulsive myoelectric alterations were observed in infected animals: the repetitive bursts of action potentials (RBAP) and periods of sustained spike potentials (SSP). Myoelectric activity from infected animals indicated decreased cycling of the interdigestive MMC. RBAP and SSP were more prevalent in the distal small intestine corresponding to tapeworm location. The percent of spike potential activity indicated that there was a reversal in the spike potential gradient on the small intestine. The number of spike potentials was maximal in caudal and minimal in oral intestine. We propose that overall localized increases in myoelectric spike potential activity represent increased contractility and decreased propulsion triggered by the presence of the tapeworm. These motility changes were surprising, since the tapeworm Hymenolepis diminuta does not penetrate the intestinal mucosa. This interaction between parasite and host may prevent expulsion of the tapeworm from the small intestine.

Effects of PGF2 alpha and of indomethacin on rabbit small and large intestinal motility in vivo

Prostaglandin F2 alpha (PGF2 alpha) has been shown to increase contractility in the small intestine and colon in vitro, and increased mucosal prostaglandin synthesis has been reported in ulcerative colitis. The purpose of this study was to determine the effects of PGF2 alpha and of indomethacin on myoelectric and contractile activity in the rabbit ileum and colon in vivo. PGF2 alpha caused an increase in spike potential frequency and contractile activity in the terminal ileum and proximal and distal colon. Indomethacin alone increased spike potential frequency and contractile activity in the terminal ileum and proximal colon but decreased myoelectric activity in the distal colon. It is concluded that PGF2 alpha may play an important role in modulating intestinal motility, especially in the distal colon but to a lesser extent in the terminal ileum and proximal colon.

Effect of anger on colon motor and myoelectric activity in irritable bowel syndrome

The present investigation was designed to study the effect of anger on colon motor and myoelectric activity in irritable bowel syndrome. Patients with irritable bowel syndrome were compared with normal controls during resting and two anger stressors: criticism of performance on an intelligence test and during a delay of assistance for a diagnostic procedure. At rest patients with irritable bowel syndrome had higher motor and spike potential activity than normal subjects; however, the difference was only significant for spike activity. Anger significantly increased colon motor and spike potential activity in the groups compared with the resting state. Patients with irritable bowel syndrome produced significantly higher motor and spike potential activity when angered. They also reported themselves to be more hostile and appeared angrier than normal controls after the study. However, they did not report themselves to be more anxious or depressed, suggesting that the observed changes in colonic function of both groups were due to anger. Patients with irritable bowel syndrome scored significantly higher than controls on the Minnesota Multiphasic Personality Inventory scales of hypochondriasis, hysteria, and depression, but these personality factors did not significantly influence their anger level before the study. The results are discussed in terms of the role of learning in the colon and the abnormal reinforcement of bowel behavior in patients with irritable bowel syndrome.

Myoelectric activity differences in acute and chronic models of lamb intestinal atresia

Clinical and experimental investigations of intestinal atresia have reduced mortality and clarified etiology. However, the morbidity of this lesion remains excessive and its pathophysiology uncertain. The purpose of this project was to produce the first long-term model of intestinal atresia and thereby to study the motility of the adapting bowel. Intestinal atresia was induced in nine fetal lambs at midgestation by mesenteric avulsion. At term, this experimental group and eight control lambs underwent resection with anastomosis, decompression gastrostomy, and implantation of electrodes proximal and distal to the anastomosis. Vigorous resuscitation and constant intensive care were critical for survival. Slow wave activity (SWA) and spike potential activity (SPA) were recorded in the first 24 hours and every 48 hours thereafter for a 6-hour interval. Three of nine lambs with atresia and five of the eight control animals survived over 48 hours (chronic). Analysis of 220 hours of recording showed, in the first 24 hours of life, a statistically significantly different SWA of 16.4 cycles/min (+/- 1.15 SD) in the chronic atretic survivors compared with 13.1 cycles/min (+/- 2.6 SD) in the acute (died less than 48 hours) atretic group (P less than .05). The SWA of the chronic atretic survivors was similar to the SWA of the chronic nonatretic control animals, 15.1 cycles/min (+/- 1.4 SD). SPA was present on the first day of life in the microintestine of the chronic atresia group in contrast to the acute animals of this study and of Doolin and Hill's previous study. Delayed function has been attributed to the absence of SPA in the microintestine of acute models.(ABSTRACT TRUNCATED AT 250 WORDS)

Post-prandial colonic spike potential activity in the infant rhesus primate simulates adult patterns

Post-prandial colonic spike potential activity in the infant rhesus primate simulates adult patterns

Relations between Na +, Ca 2+ and K + extracellular concentrations and the effects of PGE 2 on the longitudinal muscle of the guinea pig Caecum

Prostaglandin E 2 (PGE 2) stimulated the electrical and contractile activities of the isolated longitudinal muscle of the guinea pig caecum. Pretreatment of the smooth muscle strips with Na +-deficient solutions decreased the stimulant effects of PGE 2. The action of PGE 2 was abolished on the background of high K + and low Na + solutions. A reduction of extracellular Ca 2+ to 0.2 mM did not change significantly the responses to PGE 2. The addition of D-600 depressed both spike potential activity and contractions and only a weak depolarization occurred after PGE 2. However, the effects of PGE 2 were not completely inhibited after removing Ca 2+ from the solution. These observations show that the stimulant effects of PGE 2 on the longitudinal muscle of the guinea pig caecum depend mainly on the extracellular concentration of Na + and are less sensitive to the lack of Ca 2+. It is suggested that under certain conditions Na + may transfer currents through the calcium ion channels in the smooth muscle membrane.

Identification of muscarinic receptor subtype mediating colonic response to eating

The colonic motor response to eating requires cholinergic transmission. Recent studies have identified two subclasses of muscarinic receptor, the M1 and the M2 subtype. The aim of this study was to evaluate the muscarinic receptor subtype responsible for mediating the gastrocolonic response. Spike potential (SP) activity and intraluminal pressure were recorded, during fasting and after eating a 1000-kcal mixed meal, from the distal colon of 10 healthy volunteers. In each subject three paired studies were carried out: either atropine (a nonselective antimuscarinic, 1 mg), pirenzepine (a selective M1 antimuscarinic, 10 mg), or saline were infused intravenously before eating, using a double-blind crossover design. The meal significantly increased colonic spike potential activity (17.6 +/- 3.9, SP/30 min) above fasting values (2.7 +/- 0.6, P less than 0.01) in the control study. There was no postprandial increase in spike potential activity (3.3 +/- 0.9, SP/30 min) after atropine. The meal also significantly increased spike potential activity (15.4 +/- 3.3 SP/30 min, P less than 0.01) above fasting levels and equal to that of the controls, in the pirenzepine study. These data suggest that the colonic motor response to eating is mediated through the M2 but not the M1 subtype of muscarinic receptors.

EFFECTS OF VAGOTOMY ON GASTROINTESTINAL MYOELECTRIC PATTERN OF THE CONSCIOUS DOG

The gastrointestinal myoelectric activity of conscious dogs was recorded by means of chronically implanted electrodes before and after vagotomy. In healthy, conscious, intact dogs, digestive and interdigestive patterns of the myoelectric activity were recognized in the stomach and small bowel. The gastric digestive pattern was composed of cotinuous spike potential activity followed by intermittent spike potential activity, while the intestinal digestive pattern was characterized by intermittent spike potential activity. The interdigestive pattern of the stomach and small bowel consisted of the cyclic recurring, cadually migrating band of intense spike potential activity interrupted by inactivity and intermittent spike potential activity (interdigestive myoelectric complex). After bilateral transthoracic vagotomy, gastric component of the characteristic interdigestive pattern was not observed. The results indicated that vagal innervations have a role in controlling the gastric component of the interdigestive myoelectric complex, and that the disappeared interdigestive pattern of the stomach may play an important role in the mechanisms of gastric stasis after vagotomy.

Role of histamine H1- and H2-receptors in myoelectric activity of small bowel in the dog.

Studies were conducted in conscious dogs implanted with monopolar silver electrodes along the small intestine to determine whether the intestinal motility response to histamine is mediated by H1-receptors alone or whether H2-receptors are also involved in the response. Histamine infusion alone induced a marked increase in the appearance rate and the propagation velocity of the interdigestive myoelectric complexes (IMC). This effect was reproduced by the administration of the selective H1-receptor agonist, 2-methylhistamine, and abolished by the H1-receptor antagonist, tripelennamine. Tripelennamine alone decreased the frequency of occurrence of the IMC in fasted animals and reduced significantly the spike potential activity of the small bowel in fed dogs. Neither the H2-receptor agonist, dimaprit, nor the H2-receptor antagonist, metiamide, had any influence on the motility patterns in fasted or fed animals. We conclude that histamine influences the patterns of small bowel motility via stimulation of H1-receptors but its physiological role in modulating intestinal motility remains to be determined.

Effect of anticholinergic drugs on the electrical activity of the antrum and duodeno‐jejunum in sheep

The changes induced in the electrical activity of the small intestine by atropine sulphate, diphemanil methylsulphate, hyoscine butylbromide and prifinium bromide were studied in conscious sheep fitted with chronically implanted electrodes. Increased spike potential activity was induced by carbachol. The mean slow‐wave frequency of the antrum was 7.35 ± 0.18/min with burst of spike potentials randomly superimposed on about 63% of the slow waves. The occurrence of the spike bursts was inhibited for 18—30 min after an intravenous injection of atropine (0.75 mg/kg) and during its infusion at the rate of 0.05 mg/kg/min. The activity of the proximal part of the small intestine, which is characterized by migrating myoelectric complexes moving down slowly at hourly intervals, was replaced by irregular series consisting of spike bursts of about 3 min duration, at intervals of about 12 min for a total of 110 min. Such an effect, in which the level of spike activity was reduced, was also observed with hyoscine, diphemanil and prifinium during 80, 120 and 180 min periods respectively. The injection of carbachol was followed by continuous spike activity in which the mean spike level was nearly doubled, as occurs at the onset of diarrhoea. An inhibitory effect was observed at both antral and duodeno‐jejunal levels with the four drugs used, that of hyoscine being least marked. The effect of prifinium was more pronounced than that of atropine or diphemanil, especially on the jejunum. The results suggest that the ability of these drugs to reduce the level of spike activity accompanying disruption of migrating myoelectric complexes and to inhibit the carbachol‐induced increased level of spiking may account for the antispasmodic effects observed after the use of anticholinergic drugs in gastrointestinal disorders. Prifinium had the longest lasting effect at both antral and duodeno‐jejunal levels and seemed to be a good atropine substitute to alleviate gastro‐intestinal hypermotility.

A unique distribution of laxative-induced spike potentials from the small intestine of the dog.

The effects of castor oil and ricinoleic acid on small bowel electrical activity were studied in the fasted conscious dog and were compared to the effects elicited by two nonlaxative oils (triolein and oleic acid). Spike potential activity was monitored at two jejunal sites using unipolar recording electrodes. Castor oil, ricinoleic acid, and triolein produced an increased incidence of basic electrical rhythm (BER) with associated spike potentials when compared to a fasted control; however, the total electrical spiking activity produced by these oils was not statistically different from that induced by feeding. No treatment altered any of the characteristics of BER. A novel pattern of electrical spiking activity was observed in response to the laxatives. This pattern consisted of short repetitive bursts of spike potentials which migrated the length of the recording site. The laxative-induced electrical pattern persisted for several days after treatment with ricinoleic acid or castor oil, and interdigestive patterns were occasionally interrupted for as long as 72 hr. Electrical activity following feeding or the nonlaxative oils consisted of random spike potentials, and normal interdigestive electrical activity resumed within 24 hr. The laxative-induced electrical pattern was shown to be quantitatively distinct from those produced by feeding, fasting, or nonlaxative oils. This pattern may reflect an action of these laxatives on intestinal motility during a diarrheal state.