Declarative memories

Sleep transforms the cerebral trace of declarative memories
Steffen Gais, Geneviève Albouy, Mélanie Boly, Thien Thanh Dang-Vu, Annabelle Darsaud, Martin Desseilles, Géraldine Rauchs, Manuel Schabus, Virginie Sterpenich, Gilles Vandewalle, Pierre Maquet, and Philippe Peigneux
PNAS, November 20, 2007, vol. 104, no. 47, 18778-18783.

After encoding, memory traces are initially fragile and have to be reinforced to become permanent. The initial steps of this process occur at a cellular level within minutes or hours. Besides this rapid synaptic consolidation, systems consolidation occurs within a time frame of days to years. For declarative memory, the latter is presumed to rely on an interaction between different brain regions, in particular the hippocampus and the medial prefrontal cortex (mPFC). Specifically, sleep has been proposed to provide a setting that supports such systems consolidation processes, leading to a transfer and perhaps transformation of memories. Using functional MRI, we show that postlearning sleep enhances hippocampal responses during recall of word pairs 48 h after learning, indicating intrahippocampal memory processing during sleep. At the same time, sleep induces a memory-related functional connectivity between the hippocampus and the mPFC. Six months after learning, memories activated the mPFC more strongly when they were encoded before sleep, showing that sleep leads to long-lasting changes in the representation of memories on a systems level.

Remembering the good times

Remembering the good times: neural correlates of affect regulation.
Cooney Rebecca E., Joormann Jutta, Atlas Lauren Y,Eugene Fanny, Gotlib, Ian H.
Neuroreport. 18(17):1771-1774, November 19, 2007.

Background:The ability to regulate one's mood state effectively is critical to emotional and physical health. Recent investigations have sought to delineate the neural mechanisms by which individuals regulate mood states and emotions, positing a critical role of a dorsal system that includes the dorsolateral prefrontal cortex and anterior cingulate.

Methods: This study extended these efforts by examining the neural correlates of retrieving positive autobiographical memories while experiencing a negative mood state in a sample of healthy female adults.

Results: We demonstrated that mood-incongruent recall is associated with activation in ventrolateral and ventromedial prefrontal cortices (including orbitofrontal cortex and subgenual cingulate).

Conclusions:These findings suggest that mood-incongruent recall differs from other affect regulation strategies by influencing mood through a ventral regulatory network.

Vilayanur Ramachandran: A journey to the center of your mind

(from TED) In a wide-ranging talk, Vilayanur Ramachandran explores how brain damage can reveal the connection between the internal structures of the brain and the corresponding functions of the mind. He talks about phantom limb pain, synesthesia (when people hear color or smell sounds), and the Capgras delusion, when brain-damaged people believe their closest friends and family have been replaced with imposters.