Miri Y. Neufeld

Interhemispheric correlations of slow spontaneous neuronal fluctuations revealed in human sensory cortex

Animal studies have shown robust electrophysiological activity in the sensory cortex in the absence of stimuli or tasks. Similarly, recent human functional magnetic resonance imaging (fMRI) revealed widespread, spontaneously emerging cortical fluctuations. However, it is unknown what neuronal dynamics underlie this spontaneous activity in the human brain. Here we studied this issue by combining bilateral single-unit, local field potentials (LFPs) and intracranial electrocorticography (ECoG) recordings in individuals undergoing clinical monitoring. We found slow (<0.1 Hz, following 1/f-like profiles) spontaneous fluctuations of neuronal activity with significant interhemispheric correlations. These fluctuations were evident mainly in neuronal firing rates and in gamma (40–100 Hz) LFP power modulations. Notably, the interhemispheric correlations were enhanced during rapid eye movement and stage 2 sleep. Multiple intracranial ECoG recordings revealed clear selectivity for functional networks in the spontaneous gamma LFP power modulations. Our results point to slow spontaneous modulations in firing rate and gamma LFP as the likely correlates of spontaneous fMRI fluctuations in the human sensory cortex.

Neural “Ignition”: Enhanced Activation Linked to Perceptual Awareness in Human Ventral Stream Visual Cortex

Human recognition performance is characterized by abrupt changes in perceptual states. Understanding the neuronal dynamics underlying such transitions could provide important insights into mechanisms of recognition and perceptual awareness. Here we examined patients monitored for clinical purposes with multiple subdural electrodes. The patients participated in a backward masking experiment in which pictures of various object categories were presented briefly followed by a mask. We recorded ECoG from 445 electrodes placed in 11 patients. We found a striking increase in gamma power (30-70 Hz) and evoked responses specifically associated with successful recognition. The enhanced activation occurred 150-200 ms after stimulus onset and consistently outlasted the stimulus presentation. We propose that the gamma and evoked potential activations reflect a rapid increase in recurrent neuronal activity that plays a critical role in the emergence of a recognizable visual percept in conscious awareness.

Bilateral hippocampal lesion and a selective impairment of the ability for mental time travel

Mental time travel allows individuals to mentally project themselves backwards and forwards in subjective time. This case report describes a young woman suddenly rendered amnesic as a result of bilateral hippocampal damage following an epileptic seizure and brain anoxia. Her neuropsychological profile was characterized by a high-average general level of cognitive functioning, selective deficit in episodic memory of past events and a significant difficulty to envisage her personal future. This case provides clinical support for the concept of mental time travel with its retrospective and prospective components and for the hippocampus being its critical neural substrate.

Enhanced Category Tuning Revealed by Intracranial Electroencephalograms in High-Order Human Visual Areas

The functional organization of human sensory cortex was studied by comparing intracranial EEG (iEEG) recordings of local field potentials in neurosurgical patients with functional magnetic resonance imaging (fMRI) obtained in healthy subjects. Using naturalistic movie stimuli, we found a tight correlation between these two measures throughout the human sensory cortex. Importantly, the correlation between the iEEG and fMRI signals was site-specific, exhibiting neuroanatomically specific coupling. In several cortical sites the iEEG activity was confined strictly to one object category. This site selectivity was not limited to faces but included other object categories such as houses and tools. The selectivity of the iEEG signals to images of different object categories was remarkably higher when compared with the selectivity of the corresponding fMRI signals. A plausible interpretation of the fMRI and iEEG results concerns cortical organization in which object categories are organized in a mosaic of narrowly tuned object-selective clusters.

Standardized computer-based organized reporting of EEG: SCORE.

The electroencephalography (EEG) signal has a high complexity, and the process of extracting clinically relevant features is achieved by visual analysis of the recordings. The interobserver agreement in EEG interpretation is only moderate. This is partly due to the method of reporting the findings in free‐text format. The purpose of our endeavor was to create a computer‐based system for EEG assessment and reporting, where the physicians would construct the reports by choosing from predefined elements for each relevant EEG feature, as well as the clinical phenomena (for video‐EEG recordings). A working group of EEG experts took part in consensus workshops in Dianalund, Denmark, in 2010 and 2011. The faculty was approved by the Commission on European Affairs of the International League Against Epilepsy (ILAE). The working group produced a consensus proposal that went through a pan‐European review process, organized by the European Chapter of the International Federation of Clinical Neurophysiology. The Standardised Computer‐based Organised Reporting of EEG (SCORE) software was constructed based on the terms and features of the consensus statement and it was tested in the clinical practice. The main elements of SCORE are the following: personal data of the patient, referral data, recording conditions, modulators, background activity, drowsiness and sleep, interictal findings, “episodes” (clinical or subclinical events), physiologic patterns, patterns of uncertain significance, artifacts, polygraphic channels, and diagnostic significance. The following specific aspects of the neonatal EEGs are scored: alertness, temporal organization, and spatial organization. For each EEG finding, relevant features are scored using predefined terms. Definitions are provided for all EEG terms and features. SCORE can potentially improve the quality of EEG assessment and reporting; it will help incorporate the results of computer‐assisted analysis into the report, it will make possible the build‐up of a multinational database, and it will help in training young neurophysiologists.

Assessment of neurolymphomatosis by brachial plexus biopsy and PET/CT. Report of a case.

Objective: To report a biopsy-proven neurolymphomatosis in a young woman with previous non-Hodgkin’s lymphoma (NHL) of uterine cervix.Patient: The patient presented with a painful brachial plexopathy and developed multiple cranial and spinal nerve palsies.Methods and results: The diagnosis was achieved by an open brachial plexus biopsy. A PET/CT study was used to assess the full extent of the disease and showed involvement of additional cranial nerves and spinal nerve roots. A complete although short lasting clinical and radiological response was achieved by means of systemic high dose methotrexate treatment combined with rituximab and intra-CSF injections of cytarabine.

The diagnostic aid of routine EEG findings in patients presenting with a presumed first-ever unprovoked seizure

Data are available on the yield of a single EEG recording in patients with epilepsy but there is little information on EEG findings as an aid in supporting the diagnosis of an epileptic event in patients presenting with a first-ever event suspected of being an unprovoked seizure. We retrieved files of patients above the age of 15 years admitted through the emergency room during 1991-1995 with presumed first-ever unprovoked seizure. There were 91 patients (age 50+/-24; 52 males), of whom 66% had a presumed seizure of unknown origin and 34% had presumed remote symptomatic seizures. About 80% had generalized seizures (primarily or secondarily). In all the patients an EEG had been performed within 48 h of the event. Abnormal EEGs were obtained in 69%, with epileptiform activity in 21% (10% focal, 9% generalized and 2% focal and generalized), slowing in 58% (21% focal, 31% generalized and 7% focal and generalized), and both epileptiform activity and slowing in 10%. Epileptiform activity was most common in younger patients with seizures of unknown origin, compared with older individuals with symptomatic seizures (34, 38 vs. 27%, 7%, P=0.001). We conclude that following a single unprovoked presumed seizure, adults commonly exhibit abnormalities in an EEG recorded close in time to the event. The EEG is particularly helpful in supporting the epileptic nature of the event in younger patients and in those with seizures of unknown origin.

Spatial and Object-Based Attention Modulates Broadband High-Frequency Responses across the Human Visual Cortical Hierarchy

One of the puzzling aspects in the visual attention literature is the discrepancy between electrophysiological and fMRI findings: whereas fMRI studies reveal strong attentional modulation in the earliest visual areas, single-unit and local field potential studies yielded mixed results. In addition, it is not clear to what extent spatial attention effects extend from early to high-order visual areas. Here we addressed these issues using electrocorticography recordings in epileptic patients. The patients performed a task that allowed simultaneous manipulation of both spatial and object-based attention. They were presented with composite stimuli, consisting of a small object (face or house) superimposed on a large one, and in separate blocks, were instructed to attend one of the objects. We found a consistent increase in broadband high-frequency (30–90 Hz) power, but not in visual evoked potentials, associated with spatial attention starting with V1/V2 and continuing throughout the visual hierarchy. The magnitude of the attentional modulation was correlated with the spatial selectivity of each electrode and its distance from the occipital pole. Interestingly, the latency of the attentional modulation showed a significant decrease along the visual hierarchy. In addition, electrodes placed over high-order visual areas (e.g., fusiform gyrus) showed both effects of spatial and object-based attention. Overall, our results help to reconcile previous observations of discrepancy between fMRI and electrophysiology. They also imply that spatial attention effects can be found both in early and high-order visual cortical areas, in parallel with their stimulus tuning properties.

Lateralization of deficit in self-awareness of memory in patients with intractable epilepsy

Summary:  Purpose: Memory disorders are prominent among patients with intractable epilepsy. It has, however, been frequently observed that subjective memory complaints of these patients did not match their performance on objective memory tests. This discrepancy may reflect emotional, cognitive, or self‐awareness deficits among these individuals. The aim of the current study was to explore the interference of cerebral dysfunction on accuracy of self‐appraisal for memory.

Generalized convulsive status epilepticus in Creutzfeldt–Jakob disease

We report a patient who was referred to our department because of generalized status epilepticus. His condition deteriorated rapidly and he died 1 month after admission. Autopsy confirmed the clinical diagnosis of Creutzfeldt-Jakob disease (CJD). CJD should be added to the list of rare but possible causes of generalized status epilepticus.