It is hypothesized that emotional arousal modulates long-term memory consolidation through the amygdala. Gaseous anesthetic agents are among the most potent drugs that cause temporary amnesia, yet the effects of inhalational anesthesia on human emotional memory processing remain unknown. To study this, two experiments were performed with the commonly used inhalational anesthetic sevoflurane. In experiment 1, volunteers responded to a series of emotional and neutral slides while under various subanesthetic doses of sevoflurane or placebo (no anesthesia). One week later, a mnemonic boost for emotionally arousing stimuli was evident in the placebo, 0.1%, and 0.2% sevoflurane groups, as measured with a recognition test. However, the mnemonic boost was absent in subjects who received 0.25% sevoflurane. Subsequently, in experiment 2, glucose PET assessed brain-state-related activity of subjects exposed to 0.25% sevoflurane. Structural equation modeling of the PET data revealed that 0.25% sevoflurane suppressed amygdala to hippocampal effective connectivity. The behavioral results show that 0.25% sevoflurane blocks emotional memory, and connectivity results demonstrate that this dose of sevoflurane suppresses the effective influence of the amygdala. Collectively, the findings support the hypothesis that the amygdala mediates memory modulation by demonstrating that suppressed amygdala effectiveness equates with a loss of emotional memory.
Figure - The cerebral metabolic effects of 0.25% sevoflurane are shown. (A) Representative high-resolution PET scans. (B) Absolute (mean ± SD) regional metabolic changes (white bars, placebo, no anesthesia; dark bars, 0.25% sevoflurane; marked with * for P less than 0.05). (C) Relative percent decreases of regional metabolism. (D) Regional SPM results of sevoflurane induced metabolic suppression (Upper, sagittal; Lower, axial). E shows the regional thalamic finding (brain center) on a colorized MRI. The SPM effects are significant at P less than 0.001, uncorrected; displayed at P less than 0.005, with a 500-voxel extent.
Monday, February 25, 2008
Watching an anesthetic block emotional memory
Here is an intriguing observation by Alkiri et al. We usually recall emotional pictures or events better than neutral ones. They found that low levels of the inhalation anesthetic sevoflurane could block this effect, and with PET imaging found a corresponding suppression of amygdala to hippocampal effective connectivity. Here is their abstract and one summary figure: