Spindles in Sleep and Awake State

The proposed project searches for a better insight into the relationship of spindles and spindle-like activity in sleep and in awake state. In sleep, spindles are predominantly seen in stage 2 having a frequency of 12-14Hz. In awake state, synchronization patterns with a frequency of 10-14Hz can be observed. Interactions in specific (relay cells) and reticular neurons of the Thalamus are supposed to play a role in the generation of both patterns. Both induced phenomena, spindles and spindle-like activity, might share the same functional role, namely the blocking of thalamocortical information transfer. Since the frequency range overlaps, it is of interest to study both phenomena with special emphasis on common features. Basic parameters (frequency, duration,...) of automatically detected sleep spindles out of whole-night polysomnograms are measured with time-frequency analysis methods. These data are used to generate a spindle prototype. To clarify the relationship of spindles and spindle-like activity, EEG data will be recorded from 15 healthy subjects in two experiments involving awake and sleeping states. In these experiments periodic visual or tactile stimulation will be applied for some hours to induce a state of drowsiness and light sleep. The recorded spindling patterns will be compared to the sleep spindle prototype with respect to their features. In two further experiments motor and verbal tasks known to produce synchronization patterns in the alpha band over sensorimotor areas will be used. The evoked response (SEP) elicited by online stimulation time- locked to the appearance of spindle-like activity will be evaluated. This is conducted in order to proof the validity of the concept of blocked thalamocortical information transfer.

The aim of project P14831-PSY was to search for a link of spindling phenomena in awake state and in sleep. Independently, these probably similar types of spindle-like activity in the human EEG during sleep, superficial sleep or in awake state have been related to a blockade of thalamo-cortical information transfer. It was of interest to investigate these phenomena to obtain a better insight in the mechanisms underlying the generation of spindling activity and to ask for the common functionality. Analysis of the EEG in real-time was used to stimulate during the occurrence of spindling activity. Several different studies were carried out in the course of the project. For this research, new software tools have been implemented. It is now possible to analyse event related phenomena (ERD/ERS) with respect to changes in different frequency bands at one glance. The validity of evoked potential studies can be evaluated online during a measurement. The Matching Pursuit algorithm, although needing high computational demands, proved to yield clearer time-frequency representations of EEG changes than wavelet analysis or Short Time Fourier Transform. A stimulation` in real-time, enabling closed loop experiments in which the machine "interacts" with the human`s EEG, has proven to be a useful tool to study cortical dynamics. Moreover, different techniques to detect spindling phenomena online have been implemented successfully. Within the project`s course, the possibility to distinguish different finger based on the frequency of induced post- stimulus ` beta oscillations (ERS) has been researched. A task dependent relationship of induced beta oscillations and evoked potentials (EP) was investigated in 10 participants. As a result, stimulus induced beta ERS was significantly attenuated during finger movement, whereas the long-latency SEP components appeared to be enhanced. A major investigation focused on possible functional similarities of alpha and beta rhythms. The beta ERS, morphologically similar to sleep spindles, was compared with alpha synchronization both task and event related using time-frequency analysis and signal power measurements. A weak suppression of the stimulation- induced beta ERS (indicating an enhanced activity state of the sensorimotor areas) during finger motor imagery has been found. Mental imagination of foot movement led to an increase of the hand area mu rhythm, but did not interfere with stimulation-related effects on beta ERS. A study researching the beta bursts after termination of movement was conducted. These beta bursts are dominant over the contralateral hand representation area, but also appear over the midcentral area `overlaying the supplementary motor area (SMA) and the foot representation area. A significant earlier onset of the beta ERS was found over the midcentral area. Another focus of the project was on real-time detection of spindle like activity. In the first online experiment, alpha bandpower together with a predetermined threshold was used to detect the occurrence of alpha synchronization in real-time. In cooperation with the Institute of Psychology in Salzburg, an online experiment to research the functional role of EEG theta was designed. The project will be continued with three additional online stimulation experiments. In the case of a reduced somatosensory evoked potential (SEP) following stimulation during spindle like activity, we can assume a cortical deactivation during SLA generation. This would fit into the framework of "gating" during spindling phenomena. So far, P14831-PSY resulted in a deeper insight into the generation and functional role of spindling phenomena in awake state. It is expected that the analysis of sleep spindling phenomena will be possible in cooperation with sleep centers, as the tools and methods are now at hand.