Neural activity in human hippocampal formation reveals the spatial context of retrieved memories.

In many species, spatial navigation is supported by a network of place cells that exhibit increased firing whenever an animal is in a certain region of an environment. Does this neural representation of location form part of the spatiotemporal context into which episodic memories are encoded? We recorded medial temporal lobe neuronal activity as epilepsy patients performed a hybrid spatial and episodic memory task. We identified place-responsive cells active during virtual navigation and then asked whether the same cells activated during the subsequent recall of navigation-related memories without actual navigation. Place-responsive cell activity was reinstated during episodic memory retrieval. Neuronal firing during the retrieval of each memory was similar to the activity that represented the locations in the environment where the memory was initially encoded.

The EPILEPSIAE database: an extensive electroencephalography database of epilepsy patients.

From the very beginning the seizure prediction community faced problems concerning evaluation, standardization, and reproducibility of its studies. One of the main reasons for these shortcomings was the lack of access to high-quality long-term electroencephalography (EEG) data. In this article we present the EPILEPSIAE database, which was made publicly available in 2012. We illustrate its content and scope. The EPILEPSIAE database provides long-term EEG recordings of 275 patients as well as extensive metadata and standardized annotation of the data sets. It will adhere to the current standards in the field of prediction and facilitate reproducibility and comparison of those studies. Beyond seizure prediction, it may also be of considerable benefit for studies focusing on seizure detection, basic neurophysiology, and other fields.

Early, partly anticipatory, neural oscillations during identification set the stage for priming.

Perceptual priming is a fundamental long-term memory capability by which exposure to a stimulus improves later perceptual processing of that stimulus. A widespread hypothesis is that priming is the later result of perceptual learning during stimulus identification. Testing this hypothesis involves isolating priming without explicit memory, and appropriately measuring brain activity during initial experimental exposure to assess whether brain activity related to identification differs as a function of later priming. Here, we show, using magnetoencephalography (MEG), that words primed in a later test are distinguished from unprimed words at initial exposure by (a) more specific responses in perceptual brain areas, indicated by an early (within 240 ms after word onset) decrease in amplitude but increase in phase alignment of beta and gamma oscillations, and (b) improved coordination of responses across perceptual and higher brain areas in the same time window, indicated by an increase in interareal phase synchrony of alpha oscillations. The increase in interareal phase synchrony partly started already in the pre-stimulus period, approximately 60-80 ms prior to word onset, showing that the improved coordination of responses across areas was partly anticipatory. The anatomy and early timing of these patterns reveal a neural link between identification and long-term memory. The pre-stimulus findings additionally show that priming is related to the stimulus-specific anticipatory state of visual identification areas at initial exposure.

The oscillatory dynamics of recognition memory and its relationship to event-related responses.

The large-scale neural dynamics underlying higher cognitive processes are characterized by at least three types of stimulus-response: (i) the resetting of ongoing oscillatory brain activity without concomitant changes in response amplitude (phase alignment response); (ii) the addition of response amplitude to the ongoing brain activity in a time-locked manner (evoked response); and (iii) the addition of response amplitude that is not time-locked (induced response). Recent animal studies identified evoked responses as a characteristic neural response during stimulus perception but leave open the possibility that higher cognition, such as memory, is characterized more predominantly by phase alignment and/or induced responses. Using whole-head single-trial magnetoencephalography data from eight healthy adults, we show that all three types of response are related to the discrimination of old and new stimuli in a visual word recognition memory paradigm. In four subjects, single-trial evoked responses were the single constituents of event-related field old/new differences that have been previously related to familiarity-based and recollection-based recognition memory. While these data show that the oscillatory brain dynamics underlying recognition memory are characterized by a complex mix of three types of stimulus-response, they also clearly implicate evoked responses in higher cognitive processes such as recognition memory.