Interactions between stimulievoked cortical activity and spontaneous low frequency oscillations measured with neuronal calcium Abstract   Spontaneous brain activity has been widely used to map brain connectivity. The interactions between taskevoked brain responses and the spontaneous cortical oscillations, especially within the low frequency range of xe2x88xbc0.1xe2x80xafHz, are not fully understood. Trialtotrial variabilities in brainu0027s response to sensory stimuli and the ability for brain to detect under noisy conditions suggest an appreciable impact of the brain state. Using a multimodality imaging platform, we simultaneously imaged neuronal Ca2 and cerebral hemodynamics at baseline and in response to singlepulse forepaw stimuli in ratu0027s somatosensory cortex. The high sensitivity of this system enables detection of responses to very weak and strong stimuli and real time determination of low frequency oscillations without averaging. Results show that the ongoing neuronal oscillations inversely modulate Ca2 transients evoked by sensory stimuli. High intensity stimuli reset the spontaneous neuronal oscillations to an unpreferable excitability following the stimulus. Cerebral hemodynamic responses also inversely interact with the spontaneous hemodynamic oscillations, correlating with the neuronal Ca2 transient changes. The results reveal competing interactions between spontaneous oscillations and stimulationevoked brain activities in somatosensory cortex and the resultant hemodynamics.

Cortical hemodynamic responses induced by lowintensity transcranial ultrasound stimulation of mouse cortex Abstract   Ultrasoundmediated neuromodulation is emerging as a key technology for targeted noninvasive brain stimulation, but key insights into its effects and doseresponse characteristics are still missing. The purpose of this study is to systematically evaluate the effect of lowintensity transcranial ultrasound stimulation (TUS) on complementary aspects of cerebral hemodynamic. We simultaneously record the EMG signal, local field potential (LFP) and cortical blood flow (CBF) using electrophysiological recording and laser speckle contrast imaging under ultrasound stimulation to simultaneously monitor motor responses, neural activities and hemodynamic changes during the application of lowintensity TUS in mouse motor cortex, using excitation pulses which caused whisker and tail movement. Our experimental results demonstrate interdependent TUSinduced motor, neural activity and hemodynamic responses that peak approximately 0.55s, 1.05s and 2.5s after TUS onset, respectively, and show a linear coupling relationship between their respective varying response amplitudes to repeated stimuli. We also found monotonic doseresponse parametric relations of the CBF peak value increase as a function of stimulation intensity and duration, while stimulus dutycycle had only a weak effect on peak responses. These findings demonstrate that TUS induces a change in cortical hemodynamics and LSCI provide a high temporal resolution view of these changes.