Dissociating retrieval success from incidental encoding activity during emotional memory retrieval, in the medial temporal lobe

Hippocampal activation and connectivity in the aging brain

The hippocampus and underlying cortices are highly susceptible to pathologic change with increasing age. Using an associative face-scene (Face-Place) encoding task designed to target these regions, we investigated activation and connectivity patterns in cognitively normal older adults. Functional MRI scans were collected in 210 older participants (mean age = 76.4 yrs) in the Baltimore Longitudinal Study of Aging (BLSA). Brain activation patterns were examined during encoding of novel Face-Place pairs. Functional connectivity of the hippocampus was also examined during encoding, with seed regions placed along the longitudinal axis in the head, body and tail of the structure. In the temporal lobe, task activation patterns included coverage of the hippocampus and underlying ventral temporal cortices. Extensive activation was also seen in frontal, parietal and occipital lobes of the brain. Functional connectivity analyses during overall encoding showed that the head of the hippocampus was connected to frontal and anterior/middle temporal regions, the body with frontal, widespread temporal and occipital regions, and the tail with posterior temporal and occipital cortical regions. Connectivity limited to encoding of subsequently remembered stimuli showed a similar pattern for the hippocampal body, but differing patterns for the head and tail regions. These results show that the Face-Place task produces activation along the occipitotemporal visual pathway including medial temporal areas. The connectivity results also show that patterns of functional connectivity vary throughout the anterior-posterior extent of the hippocampus during memory encoding. As these patterns include regions vulnerable to pathologic change in early stages of Alzheimer's disease, continued longitudinal assessment of these individuals can provide valuable information regarding changes in brain-behavior relationships that may occur with advancing age and the onset of cognitive decline.

Efficacy and brain mechanism of transcutaneous auricular vagus nerve stimulation for adolescents with mild to moderate depression: Study protocol for a randomized controlled trial

BACKGROUND

Depression is a common mental illness in childhood and adolescence, with an incidence of 4%-5%; it can lead to impairments in learning and social functioning. Transcutaneous auricular vagus nerve stimulation (taVNS) is a commonly used method of auricular acupuncture point stimulation, which is regarded as an effective treatment for adults with depression. The aim of this study was to investigate the efficacy and mechanism of taVNS for adolescents with mild to moderate depression.

METHODS

This randomized controlled clinical trial will include 120 patients aged 12-16 years, all of whom are diagnosed with mild to moderate depression. Patients will be randomly assigned to a taVNS group and a drug control group (sertraline hydrochloride) at a ratio of 1:1. Patients will be evaluated using the 17-item Hamilton Depression Scale, Hamilton Anxiety Rating Scale, Self-Rating Depression Scale, Self-Rating Anxiety Scale, and Pittsburgh Sleep Quality Index scores at baseline, as well as at the 2nd, 4th, 6th, 8th, and 12th weeks. To investigate the underlying neural mechanisms of taVNS treatment from the perspective of the default mode network, multimodal magnetic resonance imaging (MRI; i.e., structural MRI [sMRI], resting state MRI [rsMRI], and pseudocontinuous arterial spin-labeled [pcASL] MRI) will be used to compare cerebral images among groups. MRI data will also be collected from 40 healthy volunteers to assess whether the participants exhibit normal development of structural and functional components.

DISCUSSION

Depression is the most common mental disorder in adolescence. Drug treatment can improve depression symptoms; however, the side effects of drug treatments are often severe. This study proposes a simple physiotherapy that aims to treat adolescents with mild to moderate depression. The mechanism of taVNS in the treatment of depression will also be investigated. The results of this study will provide evidence to guide the application of taVNS in adolescents with depression.

Brain-Derived Neurotrophic Factor Val66Met Polymorphism Is Associated With a Reduced ERP Component Indexing Emotional Recollection

The Met allele of the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism is associated with reduced functioning of the amygdala and hippocampus. It has been linked to major psychiatric conditions, including depression and post-traumatic stress disorder, and is associated with deficits in episodic memory. The precise mechanisms of the BDNF gene’s influence on emotional memory are not well characterized, especially its impact on recognition. Two electrophysiological experiments of emotional memory were run on two independent samples genotyped for BDNF Val66Met. Event-related potentials (ERPs) corresponding to the recognition of negative and neutral words (Experiment 1, N = 37) and negative and positive words (Experiment 2, N = 23) were recorded, and the late parietal component (LPC), typically associated with conscious recollection, was analyzed. In Experiment 1, a reduced LPC was observed in Met carriers (N = 12) compared to Val homozygotes (N = 25) in the negative condition, but the group difference was not present in the neutral condition. In Experiment 2, the reduced LPC was seen in Met carriers (N = 12) compared to Val homozygotes (N = 11) across both conditions. This study provides the first evidence of an association between the BDNF Val66Met genotype and the late parietal electrophysiological component, suggesting that the conscious experience of emotional recollection may differ according to BDNF Val66Met genotype. Further, these results suggest that this effect is likely due to emotional arousal rather than valence polarity. Results were discussed with reference to the possible mechanisms by which emotional recollection deficits may contribute to psychopathology.

Monetary incentives at retrieval promote recognition of involuntarily learned emotional information

Previous studies have suggested that the effects of reward on memory processes are affected by certain factors, but it remains unclear whether the effects of reward at retrieval on recognition processes are influenced by emotion. The event-related potential was used to investigate the combined effect of reward and emotion on memory retrieval and its neural mechanism. The behavioral results indicated that the reward at retrieval improved recognition performance under positive and negative emotional conditions. The event-related potential results indicated that there were significant interactions between the reward and emotion in the average amplitude during recognition, and the significant reward effects from the frontal to parietal brain areas appeared at 130-800 ms for positive pictures and at 190-800 ms for negative pictures, but there were no significant reward effects of neutral pictures; the reward effect of positive items appeared relatively earlier, starting at 130 ms, and that of negative pictures began at 190 ms. These results indicate that monetary incentives at retrieval promote recognition of involuntarily learned emotional information.

Local context influences memory for emotional stimuli but not electrophysiological markers of emotion-dependent attention

Emotional enhancement of free recall can be context dependent. It is readily observed when emotional and neutral scenes are encoded and recalled together in a “mixed” list, but diminishes when these scenes are encoded separately in “pure” lists. We examined the hypothesis that this effect is due to differences in allocation of attention to neutral stimuli according to whether they are presented in mixed or pure lists, especially when encoding is intentional. Using picture stimuli that were controlled for semantic relatedness, our results contradicted this hypothesis. The amplitude of well‐known electrophysiological markers of emotion‐related attention—the early posterior negativity (EPN), the late positive potential (LPP), and the slow wave (SW)—was higher for emotional stimuli. Crucially, the emotional modulation of these ERPs was insensitive to list context, observed equally in pure and mixed lists. Although list context did not modulate neural markers of emotion‐related attention, list context did modulate the effect of emotion on free recall. The apparent decoupling of the emotional effects on attention and memory, challenges existing hypotheses accounting for the emotional enhancement of memory. We close by discussing whether findings are more compatible with an alternative hypothesis, where the magnitude of emotional memory enhancement is, at least in part, a consequence of retrieval dynamics.

The Influences of Emotion on Learning and Memory

Emotion has a substantial influence on the cognitive processes in humans, including perception, attention, learning, memory, reasoning, and problem solving. Emotion has a particularly strong influence on attention, especially modulating the selectivity of attention as well as motivating action and behavior. This attentional and executive control is intimately linked to learning processes, as intrinsically limited attentional capacities are better focused on relevant information. Emotion also facilitates encoding and helps retrieval of information efficiently. However, the effects of emotion on learning and memory are not always univalent, as studies have reported that emotion either enhances or impairs learning and long-term memory (LTM) retention, depending on a range of factors. Recent neuroimaging findings have indicated that the amygdala and prefrontal cortex cooperate with the medial temporal lobe in an integrated manner that affords (i) the amygdala modulating memory consolidation; (ii) the prefrontal cortex mediating memory encoding and formation; and (iii) the hippocampus for successful learning and LTM retention. We also review the nested hierarchies of circular emotional control and cognitive regulation (bottom-up and top-down influences) within the brain to achieve optimal integration of emotional and cognitive processing. This review highlights a basic evolutionary approach to emotion to understand the effects of emotion on learning and memory and the functional roles played by various brain regions and their mutual interactions in relation to emotional processing. We also summarize the current state of knowledge on the impact of emotion on memory and map implications for educational settings. In addition to elucidating the memory-enhancing effects of emotion, neuroimaging findings extend our understanding of emotional influences on learning and memory processes; this knowledge may be useful for the design of effective educational curricula to provide a conducive learning environment for both traditional "live" learning in classrooms and "virtual" learning through online-based educational technologies.

The Influences of Emotion on Learning and Memory

Emotion has a substantial influence on the cognitive processes in humans, including perception, attention, learning, memory, reasoning, and problem solving. Emotion has a particularly strong influence on attention, especially modulating the selectivity of attention as well as motivating action and behavior. This attentional and executive control is intimately linked to learning processes, as intrinsically limited attentional capacities are better focused on relevant information. Emotion also facilitates encoding and helps retrieval of information efficiently. However, the effects of emotion on learning and memory are not always univalent, as studies have reported that emotion either enhances or impairs learning and long-term memory (LTM) retention, depending on a range of factors. Recent neuroimaging findings have indicated that the amygdala and prefrontal cortex cooperate with the medial temporal lobe in an integrated manner that affords (i) the amygdala modulating memory consolidation; (ii) the prefrontal cortex mediating memory encoding and formation; and (iii) the hippocampus for successful learning and LTM retention. We also review the nested hierarchies of circular emotional control and cognitive regulation (bottom-up and top-down influences) within the brain to achieve optimal integration of emotional and cognitive processing. This review highlights a basic evolutionary approach to emotion to understand the effects of emotion on learning and memory and the functional roles played by various brain regions and their mutual interactions in relation to emotional processing. We also summarize the current state of knowledge on the impact of emotion on memory and map implications for educational settings. In addition to elucidating the memory-enhancing effects of emotion, neuroimaging findings extend our understanding of emotional influences on learning and memory processes; this knowledge may be useful for the design of effective educational curricula to provide a conducive learning environment for both traditional "live" learning in classrooms and "virtual" learning through online-based educational technologies.

How Negative Social Bias Affects Memory for Faces: An Electrical Neuroimaging Study

During social interactions, we make inferences about people’s personal characteristics based on their appearance. These inferences form a potential prejudice that can positively or negatively bias our interaction with them. Not much is known about the effects of negative bias on face perception and the ability to recognize people faces. This ability was investigated by recording event-related potentials (ERPs) from 128 sites in 16 volunteers. In the first session (encoding), they viewed 200 faces associated with a short fictional story that described anecdotal positive or negative characteristics about each person. In the second session (recognition), they underwent an old/new memory test, in which they had to distinguish 100 new faces from the previously shown faces. ERP data relative to the encoding phase showed a larger anterior negativity in response to negatively (vs. positively) biased faces, indicating an additional processing of faces with unpleasant social traits. In the recognition task, ERPs recorded in response to new faces elicited a larger FN400 than to old faces, and to positive than negative faces. Additionally, old faces elicited a larger Old-New parietal response than new faces, in the form of an enlarged late positive (LPC) component. An inverse solution SwLORETA (450–550 ms) indicated that remembering old faces was associated with the activation of right superior frontal gyrus (SFG), left medial temporal gyrus, and right fusiform gyrus. Only negatively connoted faces strongly activated the limbic and parahippocampal areas and the left SFG. A dissociation was found between familiarity (modulated by negative bias) and recollection (distinguishing old from new faces).

Incidental Memory Encoding Assessed with Signal Detection Theory and Functional Magnetic Resonance Imaging (fMRI)

In functional magnetic resonance imaging (fMRI) studies that apply a “subsequent memory” approach, successful encoding is indicated by increased fMRI activity during the encoding phase for hits vs. misses, in areas underlying memory encoding such as the hippocampal formation. Signal-detection theory (SDT) can be used to analyze memory-related fMRI activity as a function of the participant’s memory trace strength (d^′). The goal of the present study was to use SDT to examine the relationship between fMRI activity during incidental encoding and participants’ recognition performance. To implement a new approach, post-experimental group assignment into High- or Low Performers (HP or LP) was based on 29 healthy participants’ recognition performance, assessed with SDT. The analyses focused on the interaction between the factors group (HP vs. LP) and recognition performance (hits vs. misses). A whole-brain analysis revealed increased activation for HP vs. LP during incidental encoding for remembered vs. forgotten items (hits > misses) in the insula/temporo-parietal junction (TPJ) and the fusiform gyrus (FFG). Parameter estimates in these regions exhibited a significant positive correlation with d^′. As these brain regions are highly relevant for salience detection (insula), stimulus-driven attention (TPJ), and content-specific processing of mnemonic stimuli (FFG), we suggest that HPs’ elevated memory performance was associated with enhanced attentional and content-specific sensory processing during the encoding phase. We provide first correlative evidence that encoding-related activity in content-specific sensory areas and content-independent attention and salience detection areas influences memory performance in a task with incidental encoding of facial stimuli. Based on our findings, we discuss whether the aforementioned group differences in brain activity during incidental encoding might constitute the basis of general differences in memory performance between HP and LP.