During NREM sleep cortical activity corresponding to EEG fast rhythms (FRs>10Hz) is interrupted by fragments of neural stillness (down-states), responsible for the negative peak within sleep slow oscillation (SSO). Researchers still debate whether the down-states spontaneously occur or need an initial overshoot in fluctuating activity. Herein, we studied temporally-isolated SSO in healthy subjects in order to identify two distinct EEG markers defining a putative initial up-state: i) a significant positive deflection and ii) an associated FR increase, before the negative peak. We found a positive bump preceding the down-state in SSOs detectable already at their cortical origin site, both during N2 and N3. This early positive deflection, concurrent with a broadband activation, is characterized by an increase of sigma activity (12-18Hz) from N2 to N3. An opposite trend was observed for sigma activity crowning the up-state following the negative peak. Also, we found: (i) FR activations during up-states up to high gamma frequencies; (ii) depressed sigma activity in after-spindle recovery phase; and (iii) tightly coordinated activities between distinct bands (12-36Hz, ~70Hz, ~85Hz and 105-125Hz). The correlation between different bands suggested a common mechanism for sigma and gamma, and the pre-down-state activation associated with the initial bump suggested an activity ignition for down-state, whose intensity is dependent on sleep stage. In conclusion, we hypothesize that FR accompanying SSO could mark i) sleep homeostatic processes, such as the regulation/stabilization of sleep, counterbalancing the detrimental effects of continuous inputs from peripheries, and ii) neural mechanisms favoring the storage of information acquired during wakefulness.

Fragments of wake-like activity frame down-states of sleep slow oscillations in humans: new vistas for studying homeostatic processes during sleep

Menicucci D.;LAURINO, MARCO;MASTORCI, FRANCESCA;SEBASTIANI, LAURA;GEMIGNANI, ANGELO
2013

Abstract

During NREM sleep cortical activity corresponding to EEG fast rhythms (FRs>10Hz) is interrupted by fragments of neural stillness (down-states), responsible for the negative peak within sleep slow oscillation (SSO). Researchers still debate whether the down-states spontaneously occur or need an initial overshoot in fluctuating activity. Herein, we studied temporally-isolated SSO in healthy subjects in order to identify two distinct EEG markers defining a putative initial up-state: i) a significant positive deflection and ii) an associated FR increase, before the negative peak. We found a positive bump preceding the down-state in SSOs detectable already at their cortical origin site, both during N2 and N3. This early positive deflection, concurrent with a broadband activation, is characterized by an increase of sigma activity (12-18Hz) from N2 to N3. An opposite trend was observed for sigma activity crowning the up-state following the negative peak. Also, we found: (i) FR activations during up-states up to high gamma frequencies; (ii) depressed sigma activity in after-spindle recovery phase; and (iii) tightly coordinated activities between distinct bands (12-36Hz, ~70Hz, ~85Hz and 105-125Hz). The correlation between different bands suggested a common mechanism for sigma and gamma, and the pre-down-state activation associated with the initial bump suggested an activity ignition for down-state, whose intensity is dependent on sleep stage. In conclusion, we hypothesize that FR accompanying SSO could mark i) sleep homeostatic processes, such as the regulation/stabilization of sleep, counterbalancing the detrimental effects of continuous inputs from peripheries, and ii) neural mechanisms favoring the storage of information acquired during wakefulness.
Menicucci, D.; Piarulli, A.; Allegrini, P.; Laurino, Marco; Mastorci, Francesca; Sebastiani, Laura; Bedini, R.; Gemignani, Angelo
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11568/191942
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