Direct Stimulation of Human Hippocampus During Verbal Associative Encoding Enhances Subsequent Memory Recollection

Previous studies have reported conflicting results regarding the effect of direct electrical stimulation of the human hippocampus on memory performance. A major function of the hippocampus is to form associations between individual elements of experience. However, the effect of direct hippocampal stimulation on associative memory remains largely inconclusive, with most evidence coming from studies employing non-invasive stimulation. Here, we therefore tested the hypothesis that direct electrical stimulation of the hippocampus specifically enhances hippocampal-dependent associative memory. To test this hypothesis, we recruited surgical patients with implanted subdural electrodes to perform a word pair memory task during which the hippocampus was stimulated. Our results indicate that stimulation of the hippocampus during encoding helped to build strong associative memories and enhanced recollection in subsequent trials. Moreover, stimulation significantly increased theta power in the lateral middle temporal cortex during successful memory encoding. Overall, our findings indicate that hippocampal stimulation positively impacts performance during a word pair memory task, suggesting that successful memory encoding involves the temporal cortex, which may act together with the hippocampus

The Timing of Anterior Communicating Artery Aneurysm Surgery: Comparison of Outcome in Early Versus Intermediate Surgery

The authors analyzed 47 cases of ruptured anterior communicating artery aneurysms during the past three years that were clipped within 14 days after initial hemorrhage, to study the influence of the timing of surgery on the development of vasospasm-related complications. Twelve patients were operated within three days after the onset of subarachnoid hemorrhage (SAH) (early group), and 35 patients were operated 4-14 days after SAH (intermediate group). For the statistical analysis the chi-square test with Yates' correction and Fisher's exact test were used. There were no statistically significant differences between the early and the intermediate groups in (1) the Hunt-Hess grade on admission and preoperatively, (2) the final outcome, (3) the presence of associated diseases, or (4) the occurrence of angiographic vasospasm. There was no difference in the preoperative medical management. The occurrence of symptomatic vasospasm or infarct was not different in the early and intermediate groups (p)0.10), nor was the occurrence of infarct in the anterior cerebral artery (ACA) or non-ACA territory (p)0.10). Laterality of infarct was not related to laterality of surgical approach in either the early or intermediate groups, nor in the whole group (p) 0.10). Hydrocephalus, rebleeding, and other complications were also not different in the early and intermediate groups. The authors did not find any evidence that in patients with ruptured anterior communicating artery aneurysms, the timing of surgery affects the development of vasospasm-related complications

Brain tumors in the mesial temporal lobe: long-term oncological outcome

Object. Surgical treatment of brain tumors in the mesial temporal lobe (MTL) is a highly demanding procedure. Only a few studies describing the surgery of MTL tumors have been reported, and they have been focused on the operative techniques and immediate results of the surgery. The authors have analyzed the long-term oncological outcome in patients with MTL tumors. Methods. Thirty-six patients with an MTL tumor were studied. The mean patient age at surgery was 32 years (range 13-62 years). The tumors were confined to the MTL (Schramm Type A) in 25 patients (69%). Extension of the tumor into the fusiform gyrus (Schramm Type C) and temporal stem (Schramm Type D) was observed in 4 and 7 patients (11 and 19%),respectively. There was a significant difference in the tumor size according to Schramm types (p = 0.001). Complete tumor resection was achieved in 26 patients (72%). All tumors were low-grade lesions except for 1 anaplastic astrocytoma. Results. After a median follow-up period of 50.5 months, 7 patients showed progression of the disease. The actuarial progression-free survival rates were 97% in the 1st year, 84% in the 2nd year, and 80% in the 5th year. The degree of tumor resection was significantly related to the tumor control failure (p = 50 years (p = 0.007, RR 8.312); and 4) short duration of epilepsy (< 6 months; p = 0.001, RR 21.54). Conclusions. Surgery is the principal treatment for MTL tumors, despite its technical difficulty. Complete tumor resection is strongly recommended for long-term tumor control. The MTL tumors are heterogeneous in their prognosis. Older age, short duration of epilepsy, and tumor size are all associated with poor outcome. Patients with these characteristics may have a more aggressive form of the disease than those with MTL tumors associated with chronic epilepsy. (DOI: 10.3171/2009.5.FOCUS09106)Uribe JS, 2009, J NEUROSURG, V110, P137, DOI 10.3171/2008.4.17508PHI JH, 2009, CANCER IN PRESSPichlmeier U, 2008, NEURO-ONCOLOGY, V10, P1025, DOI 10.1215/15228517-2008-052McGirt MJ, 2008, NEUROSURGERY, V63, P700, DOI 10.1227/01.NEU.0000325729.41085.73Schramm J, 2008, ACTA NEUROCHIR, V150, P857, DOI 10.1007/s00701-008-0013-7Smith JS, 2008, J CLIN ONCOL, V26, P1338, DOI 10.1200/JCO.2007.13.9337van Breemen MSM, 2007, LANCET NEUROL, V6, P421Schramm J, 2007, NEUROSURGERY, V60, P285, DOI 10.1227/01.NEU.0000249281.69384.D7Cataltepe O, 2005, J NEUROSURG, V102, P280Clusmann H, 2004, J NEUROL NEUROSUR PS, V75, P1589, DOI 10.1136/jnnp.2003.024208Schramm J, 2004, NEUROSURGERY, V55, P340, DOI 10.1227/01.NEU.0000129546.38675.1BDoetsch F, 2003, NAT NEUROSCI, V6, P1127, DOI 10.1038/nn1144Luyken C, 2003, EPILEPSIA, V44, P822Bauman G, 1999, INT J RADIAT ONCOL, V45, P923Lote K, 1997, J CLIN ONCOL, V15, P3129Piepmeier J, 1996, NEUROSURGERY, V38, P872Duffner PK, 1996, J NEURO-ONCOL, V28, P245Campbell JW, 1996, NEUROSURGERY, V38, P258PRAYSON RA, 1993, EPILEPSIA, V34, P609YASARGIL MG, 1992, ACTA NEUROCHIR, V118, P40YASARGIL MG, 1992, ACTA NEUROCHIR, V116, P147

Gating of memory encoding of time-delayed cross-frequency MEG networks revealed by graph filtration based on persistent homology

To explain gating of memory encoding, magnetoencephalography (MEG) was analyzed over multi-regional network of negative correlations between alpha band power during cue (cue-alpha) and gamma band power during item presentation (item-gamma) in Remember (R) and No-remember (NR) condition. Persistent homology with graph filtration on alpha-gamma correlation disclosed topological invariants to explain memory gating. Instruction compliance (R-hits minus NR-hits) was significantly related to negative coupling between the left superior occipital (cue-alpha) and the left dorsolateral superior frontal gyri (item-gamma) on permutation test, where the coupling was stronger in R than NR. In good memory performers (R-hits minus false alarm), the coupling was stronger in R than NR between the right posterior cingulate (cue-alpha) and the left fusiform gyri (item-gamma). Gating of memory encoding was dictated by inter-regional negative alpha-gamma coupling. Our graph filtration over MEG network revealed these inter-regional time-delayed cross-frequency connectivity serve gating of memory encoding

Minimum spanning tree analysis for epilepsy magnetoencephalography (MEG) data

Aim: Recently, brain network research is actively conducted through the application of graph theory. However, comparison between brain networks is subject to bias issues due to topological characteristics and heterogeneity across subjects. The minimum spanning tree (MST) is a method that is increasingly applied to overcome the thresholding problem. In this study, the aim is to use the MST analysis in comparing epilepsy patients and controls to find the differences between groups. Methods: The MST combines entities for epileptic magnetoencephalography (MEG) data. The MST was applied and compared to 21 left surgery (LT) and 21 right surgery (RT) patients with epilepsy and good postoperative prognosis and a healthy control (HC) group. MST metrics such as betweenness centrality, eccentricity, diameter, and leaf fraction, are computed and compared to describe the integration and efficiency of the network. The MST analysis is applied to each subject, and then the integrated MST is obtained using the distance concept. This approach can be advantageous when comparing the topological structure of patients to controls with the same number of nodes. Results: The HC group showed less topological change and more network efficiency than the epilepsy LT and RT groups. In addition, the posterior cingulate gyrus was found as a hub node only in the patient group in individual and integrated subject data analysis. Conclusions: This study suggests propose that the hippocampus borrows from the default network when one side fails, compensating for the weakened function

Comparison of MRI features and surgical outcome among the subtypes of focal cortical dysplasia

AbstractPurposeFocal cortical dysplasia (FCD) is the most common pathological diagnosis in patients who have undergone surgical treatment for intractable neocortical epilepsy. However, presurgical identification of MRI abnormalities in FCD patients remains difficult, and there are no highly sensitive imaging parameters available that can reliably differentiate among FCD subtypes. The purpose of our study was to investigate the surgical outcome in FCD patients with identifiable MRI abnormalities and to evaluate the prognostic role of the various MRI features and the characteristics of FCD pathology.MethodsWe retrospectively recruited epilepsy patients who had undergone surgical treatment for refractory epilepsy with focal MRI abnormalities and the pathological diagnosis of FCD. We evaluated the surgical outcome according to the pathological subtypes, and studied the prognostic roles of various MRI features. We used recently proposed three-tiered FCD classification system which included FCD type III when FCD occurs in association with other potentially epileptogenic pathologies.ResultsA total of 69 patients were included, and 68.1% of patients became seizure free. Patients with FCD type III had a lower chance for achieving seizure freedom (7/15) than in patients with isolated FCD (FCD types I and II) (40/54, p=0.044). Cortical thickness and blurring of gray–white matter junction were more common in isolated FCD than in FCD type III, but most MRI features failed to differentiate between FCD types I and II, and only the transmantle sign was specific for FCD type II. We failed to find a prognostic value of specific MRI abnormalities of prognostic value in terms of post-epilepsy surgery outcome in FCD patients.ConclusionsOur study showed that patients with FCD III have poor surgical outcome. Typical MRI features of isolated FCD such as cortical thickness and blurring of gray–white matter junction were less common in FCD type III and only transmantle sign was helpful in differentiating between FCD types I and II

Formation of visual memories controlled by gamma power phase-locked to alpha oscillations

Neuronal oscillations provide a window for understanding the brain dynamics that organize the flow of information from sensory to memory areas. While it has been suggested that gamma power reflects feedforward processing and alpha oscillations feedback control, it remains unknown how these oscillations dynamically interact. Magnetoencephalography (MEG) data was acquired from healthy subjects who were cued to either remember or not remember presented pictures. Our analysis revealed that in anticipation of a picture to be remembered, alpha power decreased while the cross-frequency coupling between gamma power and alpha phase increased. A measure of directionality between alpha phase and gamma power predicted individual ability to encode memory: stronger control of alpha phase over gamma power was associated with better memory. These findings demonstrate that encoding of visual information is reflected by a state determined by the interaction between alpha and gamma activity

Movement Type Prediction before Its Onset Using Signals from Prefrontal Area: An Electrocorticography Study

Power changes in specific frequency bands are typical brain responses during motor planning or preparation. Many studies have demonstrated that, in addition to the premotor, supplementary motor, and primary sensorimotor areas, the prefrontal area contributes to generating such responses. However, most brain-computer interface (BCI) studies have focused on the primary sensorimotor area and have estimated movements using postonset period brain signals. Our aim was to determine whether the prefrontal area could contribute to the prediction of voluntary movement types before movement onset. In our study, electrocorticography (ECoG) was recorded from six epilepsy patients while performing two self-paced tasks: hand grasping and elbow flexion. The prefrontal area was sufficient to allow classification of different movements through the area&apos;s premovement signals (-2.0 s to 0 s) in four subjects. The most pronounced power difference frequency band was the beta band (13-30Hz). The movement prediction rate during single trial estimation averaged 74% across the six subjects. Our results suggest that premovement signals in the prefrontal area are useful in distinguishing different movement tasks and that the beta band is the most informative for prediction of movement type before movement onset.open

A study on decoding models for the reconstruction of hand trajectories from the human magnetoencephalography

Decoding neural signals into control outputs has been a key to the development of brain-computer interfaces (BCIs). While many studies have identified neural correlates of kinematics or applied advanced machine learning algorithms to improve decoding performance, relatively less attention has been paid to optimal design of decoding models. For generating continuous movements from neural activity, design of decoding models should address how to incorporate movement dynamics into models and how to select a model given specific BCI objectives. Considering nonlinear and independent speed characteristics, we propose a hybrid Kalman filter to decode the hand direction and speed independently. We also investigate changes in performance of different decoding models (the linear and Kalman filters) when they predict reaching movements only or predict both reach and rest. Our offline study on human magnetoencephalography (MEG) during point-to-point arm movements shows that the performance of the linear filter or the Kalman filter is affected by including resting states for training and predicting movements. However, the hybrid Kalman filter consistently outperforms others regardless of movement states. The results demonstrate that better design of decoding models is achieved by incorporating movement dynamics into modeling or selecting a model according to decoding objectives.open0