Slow Oscillation Power Research Articles

Cortical Local Field Potential Power Is Associated with Behavioral Detection of Near-threshold Stimuli in the Rat Whisker System: Dissociation between Orbitofrontal and Somatosensory Cortices.

There is growing evidence that ongoing brain oscillations may represent a key regulator of attentional processes and as such may contribute to behavioral performance in psychophysical tasks. OFC appears to be involved in the top-down modulation of sensory processing; however, the specific contribution of ongoing OFC oscillations to perception has not been characterized. Here we used the rat whiskers as a model system to further characterize the relationship between cortical state and tactile detection. Head-fixed rats were trained to report the presence of a vibrotactile stimulus (frequency = 60 Hz, duration = 2 sec, deflection amplitude = 0.01-0.5 mm) applied to a single vibrissa. We calculated power spectra of local field potentials preceding the onset of near-threshold stimuli from microelectrodes chronically implanted in OFC and somatosensory cortex. We found a dissociation between slow oscillation power in the two regions in relation to detection probability: Higher OFC but not somatosensory delta power was associated with increased detection probability. Furthermore, coherence between OFC and barrel cortex was reduced preceding successful detection. Consistent with the role of OFC in attention, our results identify a cortical network whose activity is differentially modulated before successful tactile detection.

Timing matters: open-loop stimulation does not improve overnight consolidation of word pairs in humans.

The application of auditory clicks during non‐rapid eye movement (NREM) sleep phase‐locked to the up state of the slow oscillation (closed‐loop stimulation) has previously been shown to enhance the consolidation of declarative memories. We designed and applied sequences of three clicks during deep NREM sleep to achieve a quasi‐phase‐dependent open‐loop stimulation. This stimulation was successful in eliciting slow oscillation power in the stimulation period. Although fast and slow spindle power were markedly decreased during the stimulation period, memory consolidation did not differ from control. During putative up states fast spindle power remained, however, at control levels. We conclude that concurrence of slow oscillations and fast spindles suffices to maintain memory consolidation at control levels despite an overall decreased spindle activity.

Concurrent Synaptic and Systems Memory Consolidation during Sleep

Memories are consolidated during sleep by two apparently antagonistic processes: (1) reinforcement of memory-specific cortical interactions and (2) homeostatic reduction in synaptic efficiency. Using fMRI, we assessed whether episodic memories are processed during sleep by either or both mechanisms, by comparing recollection before and after sleep. We probed whether LTP influences these processes by contrasting two groups of individuals prospectively recruited based on BDNF rs6265 (Val66Met) polymorphism. Between immediate retrieval and delayed testing scheduled after sleep, responses to recollection increased significantly more in Val/Val individuals than in Met carriers in parietal and occipital areas not previously engaged in retrieval, consistent with "systems-level consolidation." Responses also increased differentially between allelic groups in regions already activated before sleep but only in proportion to slow oscillation power, in keeping with "synaptic downscaling." Episodic memories seem processed at both synaptic and systemic levels during sleep by mechanisms involving LTP.

Resting state low-frequency fluctuations in prefrontal cortex reflect degrees of harm avoidance and novelty seeking: an exploratory NIRS study

Harm avoidance (HA) and novelty seeking (NS) are temperament dimensions defined by Temperament and Character Inventory (TCI), respectively, reflecting a heritable bias for intense response to aversive stimuli or for excitement in response to novel stimuli. High HA is regarded as a risk factor for major depressive disorder and anxiety disorder. In contrast, higher NS is linked to increased risk for substance abuse and pathological gambling disorder. A growing body of evidence suggests that patients with these disorders show abnormality in the power of slow oscillations of resting-state brain activity. It is particularly interesting that previous studies have demonstrated that resting state activities in medial prefrontal cortex (MPFC) are associated with HA or NS scores, although the relation between the power of resting state slow oscillations and these temperament dimensions remains poorly elucidated. This preliminary study investigated the biological bases of these temperament traits by particularly addressing the resting state low-frequency fluctuations in MPFC. Regional hemodynamic changes in channels covering MPFC during 5-min resting states were measured from 22 healthy participants using near-infrared spectroscopy (NIRS). These data were used for correlation analyses. Results show that the power of slow oscillations during resting state around the dorsal part of MPFC is negatively correlated with the HA score. In contrast, NS was positively correlated with the power of resting state slow oscillations around the ventral part of MPFC. These results suggest that the powers of slow oscillation at rest in dorsal or ventral MPFC, respectively, reflect the degrees of HA and NS. This exploratory study therefore uncovers novel neural bases of HA and NS. We discuss a neural mechanism underlying aversion-related and reward-related processing based on results obtained from this study.

The Limitations of Near-Infrared Spectroscopy to Assess Cerebrovascular Reactivity

A total hemoglobin reactivity index (THx) derived from near-infrared spectroscopy (NIRS) has recently been introduced to assess cerebrovascular reactivity noninvasively. Analogously to the pressure reactivity index (PRx), THx is calculated as correlation coefficient with arterial blood pressure (ABP). However, the reliability of THx in the injured brain is uncertain. Although slow oscillations have been described in NIRS signals, their significance for assessment of autoregulation remains unclear. In the current study, we investigated the role of slow oscillations of total hemoglobin for NIRS-based cerebrovascular reactivity monitoring. This study was based on a retrospective analysis of data that were consecutively recorded for a different project published previously. Thirty-seven patients with traumatic brain injury and admitted to Addenbrooke's Neurosciences Critical Care Unit between June 2008 and June 2009 were included. After artifact removal, we performed spectral analysis of the tissue hemoglobin index (THI, a measure of oxy- and deoxygenated hemoglobin) and intracranial pressure (ICP) signal. PRx and THx were calculated as moving correlations between ICP and ABP, and THI and ABP, respectively. The agreement between PRx and THx as a function of normalized power of slow oscillations (0.015-0.055 Hz) contained in the input signals was assessed performing between-subject and within-subject correlation analyses. Furthermore, the correlation between the THx values derived from the right and left sides was analyzed. The agreement between PRx and THx depended on the power of slow oscillations in the input signals. Between-subject comparisons revealed a significant correlation between THx and PRx (r = 0.80, 95% confidence interval 0.53-0.92, P < 0.01) for patients with normalized slow wave activity >0.4 in the THI signal, compared with r = 0.07 (95% confidence interval -0.40 to 0.51, P = 0.79) in the remaining files. Furthermore, within-subject comparisons suggested that THx may be used as a substitute for PRx only when there is an at least moderate agreement (r = 0.36) between the THx values derived from the right and left sides. Our results suggest that the NIRS-based cerebrovascular reactivity index THx can be used as a noninvasive substitute for PRx, but only during phases with sufficient slow wave power in the input signal. Furthermore, a good agreement between the THx measures on both sides seems to be a prerequisite for comparison of a global (PRx) versus the more local (THx) index. Nevertheless, noninvasive assessment of cerebrovascular reactivity may be desirable in patients without ICP monitoring and help to guide ABP management in these patients.

Reduced sleep-associated consolidation of declarative memory in attention-deficit/hyperactivity disorder

Sleep supports the consolidation of declarative memory. Patients with attention-deficit/hyperactivity disorder (ADHD) are not only characterized by sleep problems but also by declarative memory deficits. Given that the consolidation of declarative memory during sleep is supported by slow oscillations, which are predominantly generated by the prefrontal cortex, and that ADHD patients display low prefrontal brain activity, we assumed that ADHD patients show reduced sleep-associated consolidation of declarative memory. The impact of sleep on the consolidation of declarative memory was examined with a picture recognition task. Twelve ADHD patients (10-16 years) and 12 healthy controls participated in two experimental conditions: in the sleep condition, learning was performed in the evening and picture recognition was tested after nocturnal sleep; in the wake condition, learning was conducted in the morning while retrieval took place after a day of wakefulness. Analyses of recognition accuracy revealed reduced sleep-associated enhancement of recognition accuracy in ADHD. While sleep-associated enhancement of recognition accuracy was correlated with slow oscillation power during non-REM sleep in healthy controls, no such correlations were observed in ADHD. These data indicate a deficit in sleep-associated consolidation of declarative memory in ADHD. Moreover, our results suggest reduced functionality of slow oscillations in sleep-associated consolidation of declarative memory in ADHD.

The Delta Eeg Power Was Increased After Motor Learning

The beneficial role of sleep in motor memory consolidation is now well documented. However, there has been only insufficient evidence to document neurophysiological mechanism of sleep, namely sleep stages and electroencephalographic pattern on memory consolidation. PURPOSE: We examined the effects of two hour daytime nap on three-ball cascade juggling. In addition, neurophysiological mechanism of sleep related to the memory consolidation was examined by recording and analyzing the EEG during sleep. METHODS: Subjects were 16 female college students. They were divided into nap group and control group. All subject practiced juggling for 15min, and juggling technique was evaluated in the morning. Subsequently, nap group took a 2 h nap while control group stayed awake. Both groups retested juggling in the evening. Before these experiments, nap group had taken 2 h nap in the same environment to compare with nap after juggling practice. Juggling comparisons were made using two-way ANOVA. The EEG was recorded at 8 scalp sites (Fz, Cz, Pz, POz, Oz, C3, C4, and A2 according to the international 10-20 system). Moreover, to examine EEG during nap more closely, EEG was subjected to fast Fourier transform (FFT) analysis. RESULTS: Nap group improve the juggling performance after 2 h nap (p < 0.001). Control group did not show the improvement. Compared to the baseline nap, sleep efficiency, total sleep time, and slow wave sleep (SWS) time was increased (p< 0.05.). Compared with baseline nap, delta EEG (1.0Hz∼4.0Hz) power and slow oscillation (0.3Hz∼1.0Hz) power during NREM sleep in after learning nap was increase (delta EEG power: p < 0.05, slow oscillation power: p < 0.1). CONCLUSIONS: This result suggested that sleep facilitate memory consolidation in three-ball cascade juggling. This may indicate that SWS facilitates motor memory consolidation during sleep, because the time of SWS increased in after motor learning nap. This result is consistent with the research of Gais et al. (2000) and Born et al. (2006). In addition, this study show delta EEG power in after motor learning nap was increased. The present study reported that delta wave and slow oscillation related to the information processing activity during SWS (Dang-Vu et al. 2008). The result of this study might involve these brain areas.

Multimodal Sensory Responses of Nucleus Reticularis Gigantocellularis and the Responses' Relation to Cortical and Motor Activation

The connectivity of large neurons of the nucleus reticularis gigantocellularis (NRGc) in the medullary reticular formation potentially allows both for the integration of stimuli, in several modalities, that would demand immediate action, and for coordinated activation of cortical and motoric activity. We have simultaneously recorded cortical local field potentials, neck muscle electromyograph (EMG), and the neural activity of medullary NRGc neurons in unrestrained, unanesthetized rats to determine whether the activity of the NRGc is consistent with the modulation of general arousal. We observed excitatory responses of individual NRGc neurons to all modalities tested: tactile, visual, auditory, vestibular, and olfactory. Excitation was directly linked to increases in neck muscle EMG amplitude and corresponded with increases in the power of fast oscillations (30 to 80 Hz) of cortical activity and decreases in the power of slow oscillations (2 to 8 Hz). Because these reticular formation neurons can respond to broad ranges of stimuli with increased firing rates associated with the initiation of behavioral responses, we infer that they are part of an elementary "first responder" CNS arousal mechanism.

Impulsivity, anxiety, and individual differences in evoked and induced brain oscillations

There is much evidence to confirm the view that slow waves of delta and theta ranges are linked to activation whereas alpha oscillations are somehow related to inhibition processes. In the domain of individual differences, impulsive behavior is frequently associated with increased spectral power of slow oscillations whereas Behavioral Inhibition (BI) may be associated with higher reactivity within alpha band. Here it is hypothesized that Impulsivity would predispose to higher responding in low frequencies whereas BI would predispose to higher responding within alpha band. In a sample of 51 subjects, evoked and induced responses to auditory stimuli were studied in two experimental sessions: 1) in a simple discrimination task and 2) in a stop-signal task in which subjects had to be ready to withdraw the prepared motor response . Impulsive subjects showed higher baseline delta, theta and alpha power and higher magnitude of induced responses in low frequencies. They also showed lower phase-locking in low frequencies to auditory stimuli and higher phase-locking to the overt behavioral response onset. High BI scorers showed higher baseline alpha power and higher desynchronization in this frequency band in response to stimuli. The reported findings appear to support the idea that low frequency oscillations are associated with behavioral approach and alpha with behavioral inhibition tendencies but these associations are only valid for induced responses to stimuli.