MERCOLEDI' 5 OTTOBRE SALA C ORE 9 - Avenue media

IL RUOLO DI CONTROLLO DEL TALAMO NELLA SALVAGUARDIA DEL SONNO:
UN REPORT F-MR
A Del Felice a , E Formaggio b , SF Storti a , A Fiaschi a,b , P Manganotti a,b
a Department of Neurological, Neuropsychological, Morphological and Movement Sciences,
Section of Neurology, University of Verona; b Department of Neurophysiology, IRCCS San
Camillo, Venezia
Objective: neuroimaging is an innovative technique to study brain functiong during sleep.
Most data regard nuclear neuroimaging, and only recently the potentials of functional
Magnetic Resonance (fMRI) have been applied. Materials and methods: during an fMRI
recording acquired on a 3 T scanner (MAGNETOM Allegra, Siemens, Erlangen, Germany)
with contemporary electrical stimulation at the right median nerve at different frequencies
(3 and 10 Hz), two subjects fell asleep during the 3Hz session, and woke up when the
frequency was shifted to 10 Hz. Functional data were analyzed using BrainVoyager and
activated voxels identified with a GLM approach. Results: During electrical stimulation,
subjects reported falling asleep, and were not responsive to commands. While asleep,
BOLD signal increase was evident in thalamus, ascending-reticular-system and
cerebellum, while BOLD signal decrease was observed over the bilateral occipital
(Brodman areas 18 and 19), temporal (41) and posterior parietal cortex (7), with a minor
area in the supplementary motor (6) and motor cortex (4). During wake, BOLD signal
increase was recognized in the controlateral supplementary motor area (6), contralateral
primary somatosensory cortex (7), bilateral secondary somatosensory cortex (5), bilateral
insula and cerebellum. Discussion and conclusion: We report the first cases of fMRI of
spontaneously sleeping healthy subjects during somato-sensory stimulation. A dissociation
of BOLD signal activation/deactivation emerges: increased metabolism in thalamus and
ascending-reticular-activating-system versus a BOLD decrease in heteromodal associative
cortex (visual, auditory, parietal, prefrontal). This may be a visual rendering of the
―thalamic gating hypothesis ‖ of the sleeping brain. Reduced brain responsiveness during
sleep depends on the disruption of signal transmission from the periphery to the cortex. As
an integrating station of the sensitive pathways, the thalamus selects information to be
projected or not to the pertinent cortices: in short, it protects the sleeping cortex. A limit of
our data is the lack of EEG-coregistration. Sleep was recognized by the examiner and
referred by subjects. Nonetheless, we can reliably belive the subjects fell asleep due to the
activation-deactivation pattern congruent with previous data and the BOLD pattern
mismatch between the wake/asleep scans.
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