Resting brain activity varies with dream recall frequency between subjects

Abstract

Dreaming is still poorly understood. Notably, its cerebral underpinning remains unclear. Neuropsychological studies have shown that lesions in the temporoparietal junction (TPJ) and/or the white matter of the medial prefrontal cortex (MPFC) lead to the global cessation of dream reports, suggesting that these regions of the default mode network have key roles in the dreaming process (forebrain 'dream-on' hypothesis). To test this hypothesis, we measured regional cerebral blood flow (rCBF) using [(15)O]H2O positron emission tomography in healthy subjects with high and low dream recall frequencies (DRFs) during wakefulness (rest) and sleep (rapid eye movement (REM) sleep, N2, and N3). Compared with Low recallers (0.5 ± 0.3 dream recall per week in average), High recallers (5.2 ± 1.4) showed higher rCBF in the TPJ during REM sleep, N3, and wakefulness, and in the MPFC during REM sleep and wakefulness. We demonstrate that the resting states of High recallers and Low recallers differ during sleep and wakefulness. It coheres with previous ERP results and confirms that a high/low DRF is associated with a specific functional organization of the brain. These results support the forebrain 'dream-on' hypothesis and suggest that TPJ and MPFC are not only involved in dream recall during wakefulness but also have a role in dreaming during sleep (production and/or encoding). Increased activity in the TPJ and MPFC might promote the mental imagery and/or memory encoding of dreams. Notably, increased activity in TPJ might facilitate attention orienting toward external stimuli and promote intrasleep wakefulness, facilitating the encoding of the dreams in memory.

Figure 1

Experimental design. The subjects were sleep deprived the night before the positron emission tomography (PET) acquisition. In the evening, the subjects underwent a neuropsychological assessment. In the morning, an anatomical magnetic resonance imaging (MRI) was acquired. In the afternoon, the subjects were polysomnographically monitored in the PET scan during resting. The scans were acquired during resting in different sleep stages (N2, N3, and rapid eye movement (REM) sleep) and during post-sleep wakefulness. At the end of the experiment, the subjects (High recallers and Low recallers) were asked to recall their dreams.

Figure 2

Regional cerebral blood flow (rCBF) differences in temporoparietal junction (TPJ) between High recallers and Low recallers during rapid eye movement (REM) sleep, N3, and wakefulness. Upper panel: Sagittal and axial sections of the brain showing foci with higher activation in High recallers than in Low recallers during REM sleep [−45 −54 28] and [−32 −67 31], N3 [63 −43 34], and wakefulness [−48 −54 28]. Foci of activation have been superimposed onto the normalized single-subject magnetic resonance imaging (MRI) provided with SPM8 at a threshold of p<0.001 uncorrected. Lower panel: Plots of the fitted response in the peak voxel for the contrast High recallers vs Low recallers in each condition. Each circle represents one scan. Red circles, scans acquired in High recallers, and black circles, scans acquired in Low recallers. MNI (Montreal Neurological Institute) coordinates are presented between brackets.

Figure 3

Regional cerebral blood flow (rCBF) differences in the medial prefrontal cortex (MPFC) between High and Low recallers during rapid eye movement (REM), sleep, and wakefulness. Upper panel: Sagittal and axial sections of the brain showing the foci with higher activation in High than in Low recallers during REM sleep [20 42 4] and wakefulness [20 33 36]. The foci of activation have been superimposed onto the single-subject magnetic resonance imaging (MRI) of SPM8 at the threshold of p<0.001 uncorrected. Lower panel. Plots of the fitted response in the peak voxel for the contrast High vs Low recallers in each condition. Each circle represents one scan. Red circles, scans acquired in High recallers, and black circles, scans acquired in Low recallers. MNI (Montreal Neurological Institute) coordinates are presented between brackets.