Abstract
Optical intrinsic signal imaging (OISi) method is an optical technique to evaluate the functional connectivity (FC) of the cortex in animals. Already, using OISi, the FC of the cortex has been measured in time or frequency domain separately, and at frequencies below 0.08 Hz, which is not in the frequency range of hemodynamic oscillations which are able to track fast cortical events, including neurogenic, myogenic, cardiac and respiratory activities. In the current work, we calculated the wavelet coherence (WC) transform of the OISi time series to evaluate the cerebral response changes in the stroke rats. Utilizing WC, we measured FC at frequencies up to 4.5 Hz, and could monitor the time and frequency dependency of the FC simultaneously. The results showed that the WC of the brain diminished significantly in ischemic motor and somatosensory cortices. According to the statistical results, the signal amplitude, responsive area size, correlation, and wavelet coherence of the motor and the somatosensory cortices for stroke hemisphere were found to be significantly lower compared to the healthy hemisphere. The obtained results confirm that the OISi-based WC analysis is an efficient method to diagnose the relative severity of infarction and the size of the infarcted region after ischemic stroke.
Highlights
Stroke is the most serious threat to the health, the fourth prominent reason for death, and the main reason for disability in the middle age and elderly people[12]
By selecting a wide frequency range based on the power spectral density (PSD) of the obtained time series (Fig. 1(e–h)), one could measure the functional connectivity (FC) in a broader frequency range than the 0.009–0.08 Hz range to assess the FCs originating from several sources of hemodynamic events
A new approach was used to measure the FC of the cortex based on the Optical intrinsic signal imaging (OISi) data after ischemic stroke induction in rats
Summary
Stroke is the most serious threat to the health, the fourth prominent reason for death, and the main reason for disability in the middle age and elderly people[12]. The changes induced in high frequency hemodynamic oscillations such as cardiac, respiration, myogenic, and neurogenic activities after the stroke could not be recognized Their FC measurements were done in the time domain only. Utilizing the new approach proposed in this study, the OISi data were used to evaluate the changes induced in neurogenic, myogenic, cardiac, and respiratory oscillations after ischemic stroke in rats. These factors may indicate the systemic regulation activities and neurovascular coupling. It is very useful for extracting frequency- and time-varying information from time series simultaneously This transform is more suitable than the other methods to separate intermittent, transient, and aperiodic signal components. It is more suitable than the other methods to analyze biological signals[26]
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