Converging experimental evidence indicates that mirror neurons in the monkey premotor area F5 encode the goals of observed motor acts [1-3]. However, it is unknown whether they also contribute to encoding the perspective from which the motor acts of others are seen. In order to address this issue, we recorded the visual responses of mirror neurons of monkey area F5 by using a novel experimental paradigm based on the presentation of movies showing grasping motor acts from different visual perspectives. We found that the majority of the tested mirror neurons (74%) exhibited view-dependent activity with responses tuned to specific points of view. A minority of the tested mirror neurons (26%) exhibited view-independent responses. We conclude that view-independent mirror neurons encode action goals irrespective of the details of the observed motor acts, whereas the view-dependent ones might either form an intermediate step in the formation of view independence or contribute to a modulation of view-dependent representations in higher-level visual areas, potentially linking the goals of observed motor acts with their pictorial aspects.

Hippocampal specimens resected to cure medically intractable temporal lobe epilepsy (TLE) provide a unique possibility to study functional consequences of morphological alterations. One intriguing alteration predominantly observed in cases of hippocampal sclerosis is an uncommon network of granule cells monosynaptically interconnected via aberrant supragranular mossy fibers. We investigated whether granule cell populations in slices from sclerotic and nonsclerotic hippocampi would develop ictaform activity when challenged by low-frequency hilar stimulation in the presence of elevated extracellular potassium concentration (10 and 12 mM) and whether the experimental activity differs according to the presence of aberrant mossy fibers.We found that ictaform activity could be evoked in slices from sclerotic and nonsclerotic hippocampi (27 of 40 slices, 14 of 20 patients; and 11 of 22 slices, 6 of 12 patients, respectively). However, the two patient groups differed with respect to the pattern of ictaform discharges and the potassium concentration mandatory for its induction. Seizure-like events were already induced with 10 mM K ϩ . They exclusively occurred in slices from sclerotic hippocampi, of which 80% displayed stimulus-induced oscillatory population responses (250 -300 Hz). In slices from nonsclerotic hippocampi, atypical negative field potential shifts were predominantly evoked with 12 mM K ϩ . In both groups, the ictaform activity was sensitive to ionotropic glutamate receptor antagonists and lowering of [Ca 2ϩ ] o . Our results show that, in granule cell populations of hippocampal slices from TLE patients, high K ϩ -induced seizure-like activity and ictal spiking coincide with basic electrophysiological abnormalities, hippocampal sclerosis, and mossy fiber sprouting, suggesting that network reorganization could play a crucial role in determining type and threshold of such activity.

Repetitive presentation of the same visual stimulus entails a response decrease in the action potential discharge of neurons in various areas of the monkey visual cortex. It is still unclear whether this repetition suppression effect is also present in single neurons in cortical premotor areas responding to visual stimuli, as suggested by the human functional magnetic resonance imaging literature. Here we report the responses of 'mirror neurons' in monkey area F5 to the repeated presentation of action movies. We find that most single neurons and the population at large do not show a significant decrease of the firing rate. On the other hand, simultaneously recorded local field potentials exhibit repetition suppression. As local field potentials are believed to be better linked to the blood-oxygen-level-dependent (BOLD) signal exploited by functional magnetic resonance imaging, these findings suggest caution when trying to derive conclusions on the spiking activity of neurons in a given area based on the observation of BOLD repetition suppression.

Blinks do not only protect the eye, but they do also correct for torsional eye position deviations by blink-associated resetting eye movements (BARMs). Although BARMs are functionally distinct from other eye movements in the torsional dimension, it has remained open if BARMs observed in the horizontal and vertical dimensions (fixational BARMs) are not simply microsaccades coinciding with blinks. We show here that fixational BARMs are functionally distinct and complementary to microsaccades in the following way: First, they compensate for large fixational error more efficiently than microsaccades, secondly, their probability to be executed in eccentric eye positions is higher, and thirdly, they reset the eyes into a position zone that is broader as compared to microsaccades. This suggests that BARMs help to keep the eyes in a working range wherein microsaccades guarantee high acuity vision. Moreover, we establish that fixational BARMs operate in a retina-centric frame.

The purpose of blinks is to keep the eyes hydrated and to protect them. Blinks are rarely noticed by the subject as blink-induced alterations of visual input are blanked out without jeopardizing the perception of visual continuity, features blinks share with saccades. Although not perceived, the blink-induced disconnection from the visual environment leads to a loss of information. Therefore there is critical need to minimize it. Here we demonstrate evidence for a new type of eye movement serving a distinct oculomotor demand, namely the resetting of eye torsion, likewise inevitably causing a loss of visual information. By integrating this eye movement into blinks, the inevitable down times of vision associated with each of the two behaviors are synchronized and the overall downtime minimized.DOI: http://dx.doi.org/10.7554/eLife.16290.001

BackgroundFalls frequency increases with age and particularly in neurogeriatric cohorts. The interplay between eye movements and locomotion may contribute substantially to the occurrence of falls, but is hardly investigated. This paper provides an overview of current approaches to simultaneously measure eye and body movements, particularly for analyzing the association of vestibulo-ocular reflex (VOR) suppression, postural deficits and falls in neurogeriatric risk cohorts. Moreover, VOR suppression is measured during head-fixed target presentation and during gaze shifting while postural control is challenged. Using these approaches, we aim at identifying quantitative parameters of eye-head-coordination during postural balance and gait, as indicators of fall risk.Methods/DesignPatients with Progressive Supranuclear Palsy (PSP) or Parkinson’s disease (PD), age- and sex-matched healthy older adults, and a cohort of young healthy adults will be recruited. Baseline assessment will include a detailed clinical assessment, covering medical history, neurological examination, disease specific clinical rating scales, falls-related self-efficacy, activities of daily living, neuro-psychological screening, assessment of mobility function and a questionnaire for retrospective falls. Moreover, participants will simultaneously perform eye and head movements (fixating a head-fixed target vs. shifting gaze to light emitting diodes in order to quantify vestibulo-ocular reflex suppression ability) under different conditions (sitting, standing, or walking). An eye/head tracker synchronized with a 3-D motion analysis system will be used to quantify parameters related to eye-head-coordination, postural balance, and gait. Established outcome parameters related to VOR suppression ability (e.g., gain, saccadic reaction time, frequency of saccades) and motor related fall risk (e.g., step-time variability, postural sway) will be calculated. Falls will be assessed prospectively over 12 months via protocols and monthly telephone interviews.DiscussionThis study protocol describes an experimental setup allowing the analysis of simultaneously assessed eye, head and body movements. Results will improve our understanding of the influence of the interplay between eye, head and body movements on falls in geriatric high-risk cohorts.Electronic supplementary materialThe online version of this article (doi:10.1186/s12883-015-0447-5) contains supplementary material, which is available to authorized users.

Although the eponym "West syndrome" is used widely for infantile spasms, the originators of the term and the time frame of its initial use are not well known. This article provides historical details about Dr. West, about his son who had infantile spasms, and about the circumstances leading to the coining of the term West syndrome.

In the search for the function of mirror neurons, a previous study reported that F5 mirror neuron responses are modulated by the value that the observing monkey associates with the grasped object. Yet we do not know whether mirror neurons are modulated by the expected reward value for the observer or also by other variables, which are causally dependent on value (e.g. motivation, attention directed at the observed action, arousal). In order to clarify this, we trained two rhesus macaques to observe a grasping action on an object kept constant, followed by 4 fully predictable outcomes of different values (two outcomes with positive and two with negative emotional valence). We found a consistent order in population activity of both mirror and non-mirror neurons, that matches the order of the value of this predicted outcome but that does not match the order of the above-mentioned value-dependent variables. These variables were inferred from the probability not to abort a trial, saccade latency, modulation of eye position during action observation, heart rate and pupil size. Moreover, we found subpopulations of neurons tuned to each of the 4 predicted outcome values. Multidimensional scaling revealed equal normalized distances of 0.25 between the two positive and between the two negative outcomes suggesting the representation of a relative value, scaled to the task setting. We conclude that F5 mirror neurons and non-mirror neurons represent the observer's predicted outcome value, that in the case of mirror neurons may be transferred to the observed object or action.