Cue overlap supports preretrieval selection in episodic memory: ERP evidence

People often want to recall events of a particular kind, but this selective remembering is not always possible. We contrasted two candidate mechanisms: the overlap between retrieval cues and stored memory traces, and the ease of recollection. In two preregistered experiments (Ns = 28), we used event-related potentials (ERPs) to quantify selection occurring before retrieval and the goal states — retrieval orientations — thought to achieve this selection. Participants viewed object pictures or heard object names, and one of these sources was designated as targets in each memory test. We manipulated cue overlap by probing memory with visual names (Experiment 1) or line drawings (Experiment 2). Results revealed that regardless of which source was targeted, the left parietal ERP effect indexing recollection was selective when test cues overlapped more with the targeted than non-targeted information, despite consistently better memory for pictures. ERPs for unstudied items also were more positive-going when cue overlap was high, suggesting that engagement of retrieval orientations reflected availability of external cues matching the targeted source. The data support the view that selection can act before recollection if there is sufficient overlap between retrieval cues and targeted versus competing memory traces.

Theta and gamma hippocampal-neocortical oscillations during the episodic-like memory test: impairment in epileptogenic rats

Cortical oscillations in different frequency bands have been shown to be intimately involved in exploration of environment and cognition. Here, the local field potentials in the hippocampus, the medial prefrontal cortex (mPFC), and the medial entorhinal cortex (mEC) were recorded simultaneously in rats during the execution of the episodic-like memory task. The power of hippocampal theta (~4-10 Hz), slow gamma (~25-50 Hz), and fast gamma oscillations (~55-100 Hz) was analyzed in all structures examined. Particular attention was paid to the theta coherence between three mentioned structures. The modulation of the power of gamma rhythms by the phase of theta cycle during the execution of the episodic-like memory test by rats was also closely studied. Healthy rats and rats one month after kainate-induced status epilepticus (SE) were examined. Paroxysmal activity in the hippocampus (high amplitude interictal spikes), excessive excitability of animals, and the death of hippocampal and dentate granular cells in rats with kainate-evoked SE were observed, which indicated the development of seizure focus in the hippocampus (epileptogenesis). One month after SE, the rats exhibited a specific impairment of episodic memory for the what-where-when triad: unlike healthy rats, epileptogenic SE animals did not identify the objects during the test. This impairment was associated with the changes in the characteristics of theta and gamma rhythms and specific violation of theta coherence and theta/gamma coupling in these structures in comparison with the healthy animals. We believe that these disturbances in the cortical areas play a role in episodic memory dysfunction in kainate-treated animals. These findings can shed light on the mechanisms of cognitive deficit during epileptogenesis.

Avoidance and overgeneral memory

<p>Overgeneral memory is a phenomenon that occurs in depression in which people tend to remember temporally non-specific autobiographical memories. Overgeneral memory may be functional; by avoiding specific memories, potentially distressing emotions can avoided. This “functional avoidance” may be part of a repertoire of avoidance strategies people use when they are under stress. The question of the relationship between avoidance, stress, and overgeneral memory has been investigated using only laboratory-based stressors, and no previous research has examined the relationships in both non-clinical and clinical samples. Across four studies, this thesis investigated the relationships between avoidance and overgeneral memory in clinical and non-clinical samples and whether every-day stress moderates this relationship. Studies 1, 2, and 4 engaged undergraduate samples in which mean depression scores were low (non-clinical samples). Study 3 engaged a sample from a university counselling service in which the mean depression score was high (clinical sample). Participants completed self-report measures of avoidance and stress. They were also asked to remember specific events to a series of emotion cue words on the Autobiographical Memory Test (AMT). This thesis also investigated the possibility that avoidance may be associated with a reduction in memory performance on other tests of autobiographical memory besides the AMT, perhaps because other types of memories, not just specific, can be distressing. Thus, in Study 1, participants also completed the Autobiographical Memory Test-Reversed (AMT-R) in which they were asked to retrieve general memories. In addition, across studies, the pleasantness of events remembered to positive and negative cues was examined. In Study 4, the possible moderating role of rating pleasantness on the relationship between avoidance and overgeneral memory was examined. Results from the non-clinical samples indicated higher avoidance was associated with less overgeneral remembering on the AMT. In the clinical sample, there were no significant relationships between avoidance and overgeneral memory. There were no significant relationships between avoidance and AMT-R performance. Overall, stress did not moderate the relationship between avoidance and overgeneral memory. Mean pleasantness ratings for events remembered to positive and negative cues were congruent with cue valence. However, individual positive and negative cues did not always elicit memories for pleasant and unpleasant events, respectively. Rating (vs. not rating) the pleasantness of remembered events did not moderate the relationship between avoidance and overgeneral memory. Overall, findings suggested that functional avoidance is not part of a repertoire of avoidance strategies. Ironic process theory is discussed as an explanation for why higher avoidance was associated with a lower proportion of overgeneral memories in the non-clinical samples.</p>

Clothianidin and Thiacloprid Mixture Administration Induces Degenerative Damage in the Dentate Gyrus and Alteration in Short-Term Memory in Rats

Neonicotinoids are pesticides that act as agonists of nicotinic receptors for acetylcholine in insects’ central nervous system (CNS). Chronic exposure to neonicotinoids in humans is related to autism, memory loss, and finger tremor. In this article, we evaluate the effect of subchronic oral administration of two neonicotinoids in the same mixture: clothianidin and thiacloprid. Decreasing doses of both pesticides were administered to rats starting from the lethal dose 50 (LD50) reported by the manufacturer. Our results indicate that the administration of three doses of decreasing amounts of LD50 (5/10, 4/10, and 3/10 LD50) resulted in 100% death in all cases. Ten administration times of 2/10 LD50 of the mixture caused only 20% of death cases after twenty-seven days, which was determined as a subchronic administration scheme. The animals administered 2/10 LD50 showed behavioral alterations after the first and second administration. Electrographic studies showed abnormal discharge patterns in the CNS. 72 h after the tenth dose, learning and memory tests were performed in the Morris water maze. Our results revealed significant decreases in permanence at the quadrant and the number of crosses ( P = 0.0447 , P = 0.0193 , respectively), which represent alterations in the short-term memory test, but there were no significant changes in a long-term memory test. Likewise, the brains of these animals showed tissue architecture loss, nucleosomal retraction, and a significant increase in the pycnosis of the granular neurons of the dentate gyrus analyzed at 72 h after the last dose ( P = 0.0125 ). Toxic effects and cognitive deterioration that have been found in communities living near contaminated areas are probably related to the agricultural use of neonicotinoids.

Avoidance and overgeneral memory

<p>Overgeneral memory is a phenomenon that occurs in depression in which people tend to remember temporally non-specific autobiographical memories. Overgeneral memory may be functional; by avoiding specific memories, potentially distressing emotions can avoided. This “functional avoidance” may be part of a repertoire of avoidance strategies people use when they are under stress. The question of the relationship between avoidance, stress, and overgeneral memory has been investigated using only laboratory-based stressors, and no previous research has examined the relationships in both non-clinical and clinical samples. Across four studies, this thesis investigated the relationships between avoidance and overgeneral memory in clinical and non-clinical samples and whether every-day stress moderates this relationship. Studies 1, 2, and 4 engaged undergraduate samples in which mean depression scores were low (non-clinical samples). Study 3 engaged a sample from a university counselling service in which the mean depression score was high (clinical sample). Participants completed self-report measures of avoidance and stress. They were also asked to remember specific events to a series of emotion cue words on the Autobiographical Memory Test (AMT). This thesis also investigated the possibility that avoidance may be associated with a reduction in memory performance on other tests of autobiographical memory besides the AMT, perhaps because other types of memories, not just specific, can be distressing. Thus, in Study 1, participants also completed the Autobiographical Memory Test-Reversed (AMT-R) in which they were asked to retrieve general memories. In addition, across studies, the pleasantness of events remembered to positive and negative cues was examined. In Study 4, the possible moderating role of rating pleasantness on the relationship between avoidance and overgeneral memory was examined. Results from the non-clinical samples indicated higher avoidance was associated with less overgeneral remembering on the AMT. In the clinical sample, there were no significant relationships between avoidance and overgeneral memory. There were no significant relationships between avoidance and AMT-R performance. Overall, stress did not moderate the relationship between avoidance and overgeneral memory. Mean pleasantness ratings for events remembered to positive and negative cues were congruent with cue valence. However, individual positive and negative cues did not always elicit memories for pleasant and unpleasant events, respectively. Rating (vs. not rating) the pleasantness of remembered events did not moderate the relationship between avoidance and overgeneral memory. Overall, findings suggested that functional avoidance is not part of a repertoire of avoidance strategies. Ironic process theory is discussed as an explanation for why higher avoidance was associated with a lower proportion of overgeneral memories in the non-clinical samples.</p>