Browsing by Subject "HZ"

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  • Illman, Mia; Laaksonen, Kristina; Liljeström, Mia; Jousmäki, Veikko; Piitulainen, Harri; Forss, Nina (2020)
    Modulation of the ∼20-Hz brain rhythm has been used to evaluate the functional state of the sensorimotor cortex both in healthy subjects and patients, such as stroke patients. The ∼20-Hz brain rhythm can be detected by both magnetoencephalography (MEG) and electroencephalography (EEG), but the comparability of these methods has not been evaluated. Here, we compare these two methods in the evaluating of ∼20-Hz activity modulation to somatosensory stimuli. Rhythmic ∼20-Hz activity during separate tactile and proprioceptive stimulation of the right and left index finger was recorded simultaneously with MEG and EEG in twenty-four healthy participants. Both tactile and proprioceptive stimulus produced a clear suppression at 300–350 ms followed by a subsequent rebound at 700–900 ms after stimulus onset, detected at similar latencies both with MEG and EEG. The relative amplitudes of suppression and rebound correlated strongly between MEG and EEG recordings. However, the relative strength of suppression and rebound in the contralateral hemisphere (with respect to the stimulated hand) was significantly stronger in MEG than in EEG recordings. Our results indicate that MEG recordings produced signals with higher signal-to-noise ratio than EEG, favoring MEG as an optimal tool for studies evaluating sensorimotor cortical functions. However, the strong correlation between MEG and EEG results encourages the use of EEG when translating studies to clinical practice. The clear advantage of EEG is the availability of the method in hospitals and bed-side measurements at the acute phase.
  • Arnulfo, Gabriele; Wang, Sheng H.; Myrov, Vladislav; Toselli, Benedetta; Hirvonen, Jonni; Fato, MM; Nobili, L; Cardinale, F; Rubino, A; Zhigalov, Alexander; Palva, Satu; Palva, Matias (2020)
    Inter-areal synchronization of neuronal oscillations at frequencies below similar to 100Hz is a pervasive feature of neuronal activity and is thought to regulate communication in neuronal circuits. In contrast, faster activities and oscillations have been considered to be largely local-circuit-level phenomena without large-scale synchronization between brain regions. We show, using human intracerebral recordings, that 100-400Hz high-frequency oscillations (HFOs) may be synchronized between widely distributed brain regions. HFO synchronization expresses individual frequency peaks and exhibits reliable connectivity patterns that show stable community structuring. HFO synchronization is also characterized by a laminar profile opposite to that of lower frequencies. Importantly, HFO synchronization is both transiently enhanced and suppressed in separate frequency bands during a response-inhibition task. These findings show that HFO synchronization constitutes a functionally significant form of neuronal spike-timing relationships in brain activity and thus a mesoscopic indication of neuronal communication per se.
  • Totah, Nelson K.; Logothetis, Nikos K.; Eschenko, Oxana (2021)
    The brainstem noradrenergic locus coeruleus (LC) is reciprocally connected with the prefrontal cortex (PFC). Coupling between LC spiking and the depolarizing phase of slow (1?2 Hz) waves in PFC field potentials during sleep and anesthesia suggests that LC drives cortical state transition. Reciprocal LC-PFC connectivity should also allow interactions in the opposing (top-down) direction, but prior work has only studied prefrontal control over LC activity using electrical or optogenetic stimulation. Here, we describe the physiological characteristics of spontaneously occurring top-down LC-PFC interactions. We recorded LC multiunit activity (MUA) simultaneously with PFC single-unit and local field potential (LFP) activity in urethane-anesthetized rats. We observed cross-regional coupling between the phase of 5-Hz oscillations in LC-MUA and the power of PFC LFP 60?200 Hz high y (hy). Transient increases in PFC hy power preceded peaks in the 5-Hz LC-MUA oscillation. Analysis of cross-regional transfer entropy demonstrated that the PFC hy transients were predictive of a transient increase in LC-MUA. An -29 ms delay between these signals was consistent with the conduction velocity from the PFC to the LC. Finally, we showed that PFC hy transients are associated with synchronized spiking of a subset (27%) of PFC single units. Our data suggest that PFC hy transients may indicate the timing of the top-down excitatory input to LC, at least under conditions when LC neuronal population activity fluctuates rhythmically at 5 Hz. Synchronized PFC neuronal spiking that occurs during hy transients may provide a previously unknown mode of top-down control over the LC. NEW & NOTEWORTHY The prefrontal cortex (PFC) is thought to control activity in the noradrenergic locus coeruleus (LC). Prior anatomical and prefrontal stimulation studies demonstrated the potential for PFC-LC interactions; however, it is unknown what types of PFC activity affect the LC. Here, we show that transient increases in PFC high y power and associated changes in PFC unit-pair synchrony are a potential sign of top-down control over the LC.
  • Hyvärinen, Petteri; Choi, Dawoon; Demarchi, Gianpaolo; Aarnisalo, Antti A.; Weisz, Nathan (2018)
    Background: Previous studies have shown that transcranial electrical stimulation can be successfully applied during simultaneous MEG measurements. In particular, using beamforming they have established that changes of stimulus induced as well as evoked activity can be inspected during transcranial alternating current stimulation (tACS). Objective/Hypothesis: We studied tACS-mediated changes of the auditory steady-state response (ASSR), hypothesizing that-due to the putatively inhibitory role of alpha oscillations-these evoked responses would be diminished. Methods: We compared ASSRs in conditions with and without 12-Hz and 6.5-Hz sinusoidal 1.5 mA tACS, applied bilaterally over temporal areas. Source-level activity was estimated using a linearly constrained minimum variance beamformer and compared across tACS conditions using paired t-tests following a condition-internal normalization procedure. Conclusions: By separating the electrical and auditory stimulation to non-overlapping parts of the frequency spectrum, we were able to compare auditory-evoked steady-state activity across tACS conditions. We observed a significant decrease in normalized ASSR power in the 12-Hz tACS condition, illustrating that tACS could induce immediate changes in auditory evoked activity. This study sets a methodology to further interrogate the causal roles of oscillatory dynamics in auditory cortices, as well as suggests perspectives for employing tACS in clinical contexts. (C) 2018 Published by Elsevier B.V.