Parietal thalamocortical circuitry in global dream cessation

Until relatively recently, the overarching agreement in the clinical literature was that total cessation of dreaming is related to posterior parietal lesions. Two recent case reports (Bischof and Bassetti, 2004; Poza and Martí-Massó, 2006), in which patients with medial occipital lesions demonstrated total cessation of dreaming, cast doubt on this clinic-anatomical correlation, and the neuropsychological theory of dreaming associated with it (Solms, 1997). In the current study, seven patients with medial occipital lesions (with posterior cerebral artery ischemic lesions) were recruited. Three patients had total dream cessation and four had intact dreaming (confirmed on REM awakening). Acute phase clinical neuroimaging was reviewed and the extent of the lesions in both groups was meticulously analysed by a neuroanatomist, who was blind to the dreaming status of each patient. The three patients with total cessation of dreaming all demonstrated posterior thalamic infarctions involving the pulvinar nucleus. All four of the patients with intact dreaming demonstrated medial temporo-occipital lesions, and none had thalamic lesions. Upon review of the source images of one of the two case studies with medial occipital damage and total dream cessation (Bischof and Bassetti, 2004), it was noted that the patient also demonstrated infarction of the pulvinar of the thalamus. The pulvinar of the thalamus has discrete thalamo-cortical connections to the parietal lobe, which it innervates. Disruption in the pulvinar of the thalamus can, therefore, reasonably be expected to result in parietal dysfunction. This study represents the largest case-report comparison in patients with REM-confirmed dream cessation with suitably circumscribed pathology. These findings cast doubt on claims of medial occipital mechanisms of dream cessation and suggest that posterior parietal circuitry remains involved