Over-activation in bilateral superior temporal gyrus correlated with subsequent forgetting effect of Chinese words

Altered neural correlates of episodic memory for food and non-food cues in females with overweight/obesity

Episodic memory formation is fundamental to cognition and plays a key role in eating behaviors, indirectly promoting the maintenance and acceleration of weight gain. Impaired episodic memory function is a hallmark of people with overweight/obesity, nevertheless, little research has been conducted to explore the effects of overweight/obesity on neural networks associated with episodic memory. The current study aimed to unravel the behavioral responses and neurocognitive mechanisms underlying the episodic memory for food and non-food cues in females with overweight/obesity. To explore this issue, a group of females with overweight/obesity (n = 26) and a group of age-matched females with healthy weight (n = 28) participated in a functional magnetic resonance imaging (fMRI) event-related episodic memory paradigm, during which pictures of palatable food and pictures of neutral daily necessities were presented. Whole-brain analyses revealed differential engagement in several neural regions between the groups during an episodic memory task. Specifically, compared to the healthy weight controls, females with overweight/obesity exhibited reduced brain activity in the temporal, parietal, and frontal regions during episodic memory encoding and successful retrieval of both food and non-food cues. Additionally, activation patterns in the left hippocampus and right olfactory cortex of females with and without overweight/obesity suggested that item memory changed according to the type of stimuli presented during item memory. Specifically, females with overweight/obesity showed greater engagement of the left hippocampus and right olfactory cortex when processing food cues, but less activation of the left hippocampus and right olfactory cortex when presented with non-food cues. Consistent with the obesity and suboptimal food-related decision theoretical model, these findings provide evidence of dissociation of the neural underpinnings of episodic memory in females with overweight/obesity and underline important effects of overweight/obesity on brain functions related to episodic memory.

Neural processes during encoding support durable memory

The ability to form durable memory is critical for human survival and development, but its underlying cognitive and neural mechanisms have not been well understood. In particular, existing studies have not clearly dissociated the neural processes supporting short- and long-duration memories. The present study addressed this issue with functional MRI and a modified subsequent memory paradigm. Participants were asked to make semantic judgment on a list of 320 words in the scanner. Half of the words were tested after a short delay (i.e., 1day, T1) and again after a long delay (i.e., 1week, T12), whereas the other half were tested only once after the long delay (T2). Materials forgotten during T1 were categorized as forgotten trials, and those remembered during T2 were categorized as long-duration trials. In contrast, trials remembered during T1 but not during T12 were categorized as short-duration trials. We found that compared to forgotten trials, short-duration trials showed decreased activation in the posterior cingulate cortex (PCC) and precuneus, which is consistent with many previous observations. Importantly, long-duration trials showed stronger activity in the left inferior frontal gyrus (LIFG) but less deactivation in the PCC relative to short-duration trials. Psychophysiological interactions (PPI) analysis revealed stronger functional connectivity between LIFG and PCC for long-duration trials than for forgotten trials. Our results suggest that strong PCC activity, in combination with strong LIFG activity, supports long-lasting memory.