In a research study published in Neurology Sept 14th 2014, (Poor sleep quality is associated with increased cortical atrophy in community-dwelling adults), scientists noted that poor sleep quality was associated with reduced volume within the right superior frontal cortex in cross-sectional analyses, and an increased rate of atrophy within widespread frontal, temporal, and parietal regions in longitudinal analyses.
Results were largely driven by correlations within adults over the age of 60, and could not be explained by variation in physical activity, BMI, or blood pressure. Sleep quality was not associated with hippocampal volume or atrophy.
However, researchers were not sure whether it was cause or effect: Poor sleep quality may be a cause or a consequence of brain atrophy, and future studies.