Almost all people experience dreaming, and many reference dreams in conversation, literature and artistic expression. An emerging field is the biology and psychology of dreaming. Recent discoveries have provided insight into the anatomical structures underlying dreams and their behavioral consequences. Scientific experiments using brain imaging and case studies describing brain pathologies have converged to allow a few conclusions about dream neurology.
Occipital and Temporal Cortical Areas
Dreams include all types of perception, including visual, auditory, olfactory, gustatory and tactile aspects. Yet vision and audition are the predominant senses in dreams. The occipital lobe, situated in the back of the brain, is considered its primary visual processing center. This area is active during dreams despite the eyes being closed. The temporal lobe, situated on the side of the brain, is considered its primary auditory processing center. Activity in this area is correlated with dream recall. A case report also supports a role for the occipital and temporal cortical areas in dreaming. In a 2006 study published in "Neurologia," J.J. Poza and Jose Felix Marti-Masso described the complete loss of dreaming in a woman who had experienced a bilateral posterior cerebral artery stroke. The posterior cerebral artery supplies blood to the back and side of the brain.
Amygdala, Orbito-Frontal Cortical and Anterior Cingulate Cortical Areas
The anatomical structures' underlying emotions are well known. Most of these locations are in the limbic system, especially in the amygdala, and they lie deep in the center of the brain. These deeper structures then project to cortical structures in the front (orbito-frontal cortex) and back (anterior cingulate cortex) of the brain. Cerebral blood flow increases in these regions during dreaming, indicating that they are responsible for the heavy emotional content of dreams.
Mesial Temporal Areas
As noted, temporal activation is correlated with dream recall. Recall involves memory systems located in the mesio-temporal areas of the brain, especially in the hippocampus. These locations are the inner portions of the temporal lobes, and they lie near the division of the left and right hemispheres. In a 2001 study published in "Neuron," Kenway Louie and Matthew A. Wilson showed that memory traces (electrical patterns of neuronal firing) formed while awake reappeared in dreams. This finding suggests that dreams play a role in memory consolidation.
Prefrontal Cortical Area
Dreams typically involve alteration of normal logic, reason and planning. These "executive functions" are mediated by the prefrontal cortex, which is situated in the back part of the frontal lobes in front of the motor and premotor areas. Neuroimaging studies, including a 1998 study by A.R. Braun et al. published in "Science," reveal a lack of activation in these brain locations during dreaming, which suggests a possible explanation for the bizarre nature of dreams.
References
- "Experimental Brain Research"; Human Brain Activity Time-Locked to Rapid Eye Movements During REM Sleep; Miyauchi et al.; February 2009
- "Brain"; Rhinal-Hippocampal Connectivity Determines Memory Formation During Sleep; Fell et al.; January 2006
- "Nature"; Functional Neuroanatomy of Human Rapid-Eye-Movement Sleep and Dreaming; Maquet et al.; September 1996
- "Neuron"; Temporally Structured Replay of Awake Hippocampal Ensemble Activity During Rapid Eye Movement Sleep; Louie and Wilson; January 2001
- "Science"; Dissociated Pattern of Activity in Visual Cortices and Their Projections During Human Rapid Eye Movement Sleep; Braun et al.; January 1998
