Amygdala and hippocampus volumetry and diffusivity in relation to dreaming

Abstract

Microstructural analyses by MRI brain scans and by DTI analysis of MR images were used to investigate the possible relationship between deep gray matter structures (amygdala and hippocampus) and dreaming in healthy subjects. Thirty-four subjects ranging in age 20s to 70s underwent to a MRI protocol for the assessment of volume and mean diffusivity (MD) in the amygdala and hippocampus and were asked to fill out a dream diary via audiotape recording upon morning awakening for two weeks. Multiple regression analyses evaluated the relationships between anatomical measures and quantitative and qualitative measures of the reported dreams. The main result points to a dissociation between some quantitative and qualitative aspects of dream reports. While the mean number of dreams recalled per day did not show any significant relationship with the neuroanatomical measures, significant associations with some qualitative features of the recalled dreams (emotional load, bizarreness, and vividness) and, to some extent, with the length of dream reports were observed. Particularly, a higher MD of the left amygdala, reflecting a decreased microstructural integrity, was associated with shorter dream reports and lower scores on emotional load. Bizarreness of dream reports was negatively correlated with the left amygdala volume and positively correlated with the right amygdala MD. Some specific, although weaker, relationships were also found between bizarreness and hippocampal measures. These findings indicate some direct relationships between volumetric and ultrastructural measures of the hippocampus-amygdala complex and specific qualitative features of dreaming.

Predicting Dream Recall: EEG Activation During NREM Sleep or Shared Mechanisms with Wakefulness?

“…In our opinion, the models based on physiological activation (Antrobus 1991;Koulack and Goodenough 1976;Rosenblatt et al 1992;Zimmerman 1970) and on shared mechanisms across wakefulness and sleep (De Gennaro et al 2011;Marzano et al 2011a;Scarpelli et al 2015a) are not mutually exclusive. A bulk of empirical evidence had made it clear that both the mechanisms underlying the encoding of episodic memory in sleep and wakefulness (De Gennaro et al 2011;Domhoff 2003;Marzano et al 2011a;Scarpelli et al 2015a;Schredl & Hoffmann 2003) and a specific electrophysiological background during sleep could affect the retrieval of the sleep mentation (De Gennaro et al 2010;Schredl 2009).…”

“…A bulk of empirical evidence had made it clear that both the mechanisms underlying the encoding of episodic memory in sleep and wakefulness (De Gennaro et al 2011;Domhoff 2003;Marzano et al 2011a;Scarpelli et al 2015a;Schredl & Hoffmann 2003) and a specific electrophysiological background during sleep could affect the retrieval of the sleep mentation (De Gennaro et al 2010;Schredl 2009). On the one hand, frontal theta oscillations during REM sleep (Marzano et al 2011a;Scarpelli et al 2015a) and lower alpha power during NREM sleep (Esposito et al 2004;Marzano et al 2011a) predict the subsequent DR, and these patterns resemble the EEG pattern observed in wakefulness during a successful performance in episodic memory tasks (Addante et al 2011;Guderian et al 2009;Klimesch 1996Klimesch , 1999Klimesch et al 1996).…”

“…Just after the nap, subjects were requested to fill out a sleep and dream diary (De Gennaro et al 2011) to collect subjective estimates of sleep characteristics (sleep onset latency, number of awakenings, total sleep time, sleep quality) and of dream recall (number of dreams recalled, bizarreness, vividness, emotional load, and dream length).…”

Right hemisphere neural activations in the recall of waking fantasies and of dreams

“…The Dream Bizarreness scale (Hobson et al, 1987) was used to score the material and calculate: bizarreness intensity (BI; the number of bizarre events in the domains of plot, cognition and affect); and bizarreness density (BD; calculated by dividing BI by the report word count). Emotional load (EL), without distinction between positive or negative affects, and visual vividness (VV) were also independently scored by the two raters on six-point Likert rating scales for each narrative (De Gennaro et al, 2011). All scripts were then read and recorded by an experimenter (R.R.)…”

“…Studies of cerebral blood flow and metabolism during rapid eye movement (REM) sleep suggested a relatively reduced activity in precuneus, dorsolateral prefrontal, posterior cingulate and parietal cortex, with increased activations in limbic and paralimbic regions including amygdala, hippocampus, anterior cingulate and orbitofrontal cortex (Dang-Vu, 2012). The limbic involvement is confirmed by the observation that volumes and microstructure of left amygdala inversely correlate, and volumes of right hippocampus directly correlate, with bizarreness in dream reports (De Gennaro et al, 2011). Nevertheless, a critical involvement of cortical areas in building the implausible story representation of dreams is suggested by the observation that some cortical lesions can impair or completely block dreaming (Nir and Tononi, 2010), also supporting the hypothesis that the modular architecture of brain functions is maintained during dreams (Desseilles et al, 2011).…”