Off to never-never land: losing consciousness to gain thought

In this issue of Brain , Smaranda Leu-Semenescu and colleagues describe one aspect of a rare and fascinating neuropsychological syndrome—auto-activation deficit (AAD)—in which patients with specific basal ganglia lesions experience an almost total loss of self-driven behaviour that can partially be reversed by external stimulation. Indeed, when questioned, some patients with AAD will consistently report a complete absence of spontaneous thoughts. For healthy individuals, spontaneous thoughts are not only a feature of waking life; they are also a common feature of that component of sleep that we call dreams. Leu-Semenescu and colleagues therefore asked whether the absence of mental content reported by patients with AAD also persisted during sleep—that is, are individuals with no spontaneous waking thoughts able to dream?As described in their article, sleep stages were recorded from each of a group of 13 patients with AAD and a group of matched healthy controls using a combination of EEG and other physiological measures. During periods of both rapid eye movement (REM) and non-REM sleep, all participants were awoken and asked to report their mental contents immediately before waking. Surprisingly, despite reporting a total absence of mental content during wakefulness, some patients with AAD nevertheless reported dream contents, primarily during REM sleep. …