Memory functioning after hippocampal removal: Does side matter?

To address the memory functioning after medial temporal lobe (MTL) surgery for refractory epilepsy and relationships with the side of the hippocampal removal, 22 patients with pharmaco-resistant epilepsy who had undergone MTL resection (10 right/12 left) at the Salpêtrière Hospital were compared with 21 matched healthy controls. We designed a specific neuropsychological binding memory test that specifically addressed hippocampal cortex functioning, and left-right material-specific lateralization. Our results showed that both left and right mesial temporal lobe removal cause a severe memory impairment, for both verbal and visual material. The removal of left medial temporal lobe causes worse memory impairment than the right removal regardless of the stimuli type (verbal or visual) questioning the theory of the hippocampal material-specific lateralization. The present study provided new evidence for the role of both hippocampus and surrounding cortices in memory-binding whatever the material type and also suggested that a left MTL removal is more deleterious for both verbal and visual episodic memory in comparison with right MTL removal.

The influence of object-location binding mental load effects on the visual N1 and N2 Event-related Potentials.

OBJECTIVE: This study aimed to analyze the effect of object-location binding on the visual working memory workload. For this study, thirty healthy subjects were recruited, and they performed the "What was where" task, which was modified to evaluated object-location binding memory. We analyzed their ERP and behavior response. RESULTS: Object memory and location memory were preserved during the task, but binding memory decreased significantly when more than four objects were presented. These results indicate that the N1 amplitude is related to the object-only load effect, and the posterior N2 amplitude is a binding-dependent ERP component.

Sharp-Wave Ripples in Primates Are Enhanced near Remembered Visual Objects.

The hippocampus plays an important role in memory for events that are distinct in space and time. One of the strongest, most synchronous neural signals produced by the hippocampus is the sharp-wave ripple (SWR), observed in a variety of mammalian species during offline behaviors, such as slow-wave sleep [1-3] and quiescent waking and pauses in exploration [4-8], leading to long-standing and widespread theories of its contribution to plasticity and memory during these inactive or immobile states [9-14]. Indeed, during sleep and waking inactivity, hippocampal SWRs in rodents appear to support spatial long-term and working memory [4, 15-23], but so far, they have not been linked to memory in primates. More recently, SWRs have been observed during active, visual scene exploration in macaques [24], opening up the possibility that these active-state ripples in the primate hippocampus are linked to memory for objects embedded in scenes. By measuring hippocampal SWRs in macaques during search for scene-contextualized objects, we found that SWR rate increased with repeated presentations. Furthermore, gaze during SWRs was more likely to be near the target object on repeated than on novel presentations, even after accounting for overall differences in gaze location with scene repetition. This proximity bias with repetition occurred near the time of target object detection for remembered targets. The increase in ripple likelihood near remembered visual objects suggests a link between ripples and memory in primates; specifically, SWRs may reflect part of a mechanism supporting the guidance of search based on past experience.

Sex differences of cognitive load effects on object-location binding memory.

In this study, we investigated where the sex differences of object-location binding memory performance were influenced by the cognitive load. We used the fractal objects version of the 'What was where?' task to measure object memory, location memory and objection-location binding memory. Cognitive load was controlled by task difficulty presented two sessions: one session randomly displayed three or four fractal objects (Session 34) and the other session four or five objects (Session 45). The results showed that females outperformed males on object-location binding memory. Interestingly, even when the four object trials were compared between Session 34 and Session 45, in which we believed that the level of difficulty was similar while cognitive load varied, the swap error of males was significantly increased in Session 45 compared to females. In conclusion, there may be sex differences in object-location binding memory and the males could be more sensitive about the cognitive load than females.

Hippocampal gamma-band Synchrony and pupillary responses index memory during visual search.

Memory for scenes is supported by the hippocampus, among other interconnected structures, but the neural mechanisms related to this process are not well understood. To assess the role of the hippocampus in memory-guided scene search, we recorded local field potentials and multiunit activity from the hippocampus of macaques as they performed goal-directed search tasks using natural scenes. We additionally measured pupil size during scene presentation, which in humans is modulated by recognition memory. We found that both pupil dilation and search efficiency accompanied scene repetition, thereby indicating memory for scenes. Neural correlates included a brief increase in hippocampal multiunit activity and a sustained synchronization of unit activity to gamma band oscillations (50-70 Hz). The repetition effects on hippocampal gamma synchronization occurred when pupils were most dilated, suggesting an interaction between aroused, attentive processing and hippocampal correlates of recognition memory. These results suggest that the hippocampus may support memory-guided visual search through enhanced local gamma synchrony. © 2016 Wiley Periodicals, Inc.

Sex differences of cognitive load effects on object-location binding memory

In this study, we investigated where the sex differences of object-location binding memory performance were influenced by the cognitive load. We used the fractal objects version of the ‘What was where?’ task to measure object memory, location memory and objection-location binding memory. Cognitive load was controlled by task difficulty presented two sessions: one session randomly displayed three or four fractal objects (Session 34) and the other session four or five objects (Session 45). The results showed that females outperformed males on object-location binding memory. Interestingly, even when the four object trials were compared between Session 34 and Session 45, in which we believed that the level of difficulty was similar while cognitive load varied, the swap error of males was significantly increased in Session 45 compared to females. In conclusion, there may be sex differences in object-location binding memory and the males could be more sensitive about the cognitive load than females.

Longitudinal investigation on the feature-binding working memory after subcortical infarction / 中华行为医学与脑科学杂志

Objective To investigate the cognitive behavioral characteristic longitudinally of the patients after subcortical infarction engaged in feature and binding working memory tasks.Methods The behavioral performances were recorded from 28 patients after subcortical infarction at the 1 st week (W1),3 rd moth (M3) and 6th month (M6) while performing color,location,and color-location binding delayed match-to-sample working memory task.25 healthy volunteers(controls) were investigated once using the same task protocol during the study period.Computer recorded the behavior reaction time and accuracy.Single factor variant analysis of repeated measurement was adopted.Results The accuracy of three memory tasks of M3 ((64.92 ± 5.47) ％ ; (92.88 ± 2.98) ％ ;(82.35 ±7.44)％) was improved than that of W1 ((61.06 ±7.78)％; (90.59 ±2.95)％; (77.06 ±5.58) ％) and the difference had statistically significant (P ＜ 0.05).But the reaction time of M3 ((868.31 ±118.91)ms; (833.37 ± 120.99) ms; (918.72 ± 101.28) ms) was shortened than that of W1 ((914.02 ±110.53) ms; (859.89 ± 139.94) ms; (1150.17 ± 92.02) ms) and the difference also had statistically significant (P ＜ 0.05).In the location-memory task,the correct rate of M6 ((93.91 ± 2.86) ％) was improved than that of M3 ((92.88 ± 2.98) ％) and the reaction time of M6 ((813.24 ± 119.54) ms) was shortened than M3 ((833.37 ±120.99) ms).M6 and M3 to be compared in the color memory task,the correct rate ((64.50 ± 4.49) ％ ; (64.92 ± 5.47) ％) and the reaction time ((866.47 ± 123.87) ms; (868.31 ± 118.91) ms) had no significant difference (P ＜ 0.05).But in the color-location binding task,the correct rate of M6 ((78.49 ± 7.85) ％) and M3 ((82.35 ± 7.44)％) to be compared had significant decreased nearly the level ((77.06 ± 5.58)％) of the stroke beginning.All behavioral performances of patients were worse than that of control subjects except the compare result of location-memory task in M6((93.91 ± 2.86) ％ ; (813.24 ± 119.54) ms).Conclusion Feature memory and binding memory had been damaged in different degrees in the patient after subcortical infarction.The binding memory had the secondary damage what might be related to the secondary nerve fiber degeneration after infarction.