Pain perception in patients with chronic disorders of consciousness: What can limbic system tell us?
Although it is believed that patients with Unresponsive Wakefulness Syndrome (UWS) do not feel pain, recent neuroimaging and neurophysiologic studies have demonstrated some residual traces of nociceptive processing.



To confirm this growing evidence, we evaluated 21 patients suffering from chronic disorders of consciousness (DOC) (both UWS, n=11, and Minimally Conscious State - MCS -, n=10), using an Event-Related Potential (ERP) Low-Resolution Brain Electromagnetic Tomography (LORETA) approach, based on nociceptive repeated laser stimulation (RLS). We delivered laser stimuli to the dorsum of both hands and analysed the γ-band LORETA activations and the ERP γ-power magnitude induced by laser stimulation, as well as the heart rate variability (HRV).



We found partially preserved cortical activations and ERP γ-power magnitude in all MCS and two UWS individuals. These effects were paralleled by a purposeful behaviour, and a reduced HRV concerning nociceptive stimulation, whereas the two UWS individuals showed no more than reflex behaviours, besides a strong limbic activation.



Some UWS patients may somehow perceive the affective components of nociceptive stimulation.



The diagnosis of functional locked-in syndrome should be taken into account when dealing with DOC differential diagnosis.
IRCCS Centro Neurolesi "Bonino-Pulejo", Messina, Italy. Electronic address: salbro77@tiscali.it.
Rocco Salvatore
RS
Calabrò
IRCCS Centro Neurolesi "Bonino-Pulejo", Messina, Italy.
Antonino
A
Naro
IRCCS Centro Neurolesi "Bonino-Pulejo", Messina, Italy.
Alfredo
A
Manuli
IRCCS Centro Neurolesi "Bonino-Pulejo", Messina, Italy.
Antonino
A
Leo
IRCCS Centro Neurolesi "Bonino-Pulejo", Messina, Italy.
Rosaria
R
De Luca
IRCCS Centro Neurolesi "Bonino-Pulejo", Messina, Italy.
Viviana
V
Lo Buono
IRCCS Centro Neurolesi "Bonino-Pulejo", Messina, Italy.
Margherita
M
Russo
IRCCS Centro Neurolesi "Bonino-Pulejo", Messina, Italy.
Alessia
A
Bramanti
IRCCS Centro Neurolesi "Bonino-Pulejo", Messina, Italy.
Placido
P
Bramanti
D000328:Adult; D005071:Evoked Potentials; D005260:Female; D065818:Gamma Rhythm; D006339:Heart Rate; D006801:Humans; D066331:Laser-Evoked Potentials; D008032:Limbic System / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D059225:Nociception; D010146:Pain / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology*; D058748:Pain Perception; D018458:Persistent Vegetative State / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology*
HRV; LORETA; Limbic system; MCS; Pain perception; UWS