EMERGING CONCEPTS OF BRAIN FUNCTION

Nonsynaptic plasticity model of long-term memory engrams

Using steady-state electrical properties of non-ohmic dendrite based on cable theory, we derive electrotonic potentials that do not change over time and are localized in space. We hypothesize that clusters of such stationary, local and permanent pulses are the electrical signatures of enduring memories which are imprinted through nonsynaptic plasticity, encoded through epigenetic mechanisms, and decoded through electrotonic processing. We further hypothesize how retrieval of an engram is made possible by integration of these permanently imprinted standing pulses in a neural circuit through neurotransmission in the extracellular space as part of conscious recall that acts as a guiding template in the reconsolidation of long-term memories through novelty characterized by uncertainty that arises when new fragments of memories reinstate an engram by way of nonsynaptic plasticity that permits its destabilization. Collectively, these findings seem to reinforce this hypothesis that electrotonic processing in non-ohmic dendrites yield insights into permanent electrical signatures that could reflect upon enduring memories as fragments of long-term memory engrams.

Surgery for dysembryoplastic neuroepithelial tumors and gangliogliomas in eloquent areas. Functional results and seizure control

INTRODUCTION

Dysembryoplastic neuroepithelial tumors and gangliogliomas are developmental glioneuronal tumors usually revealed by partial epilepsy. High epileptogenicity, childhood epilepsy onset, drug-resistance, temporal location, and seizure freedom after complete resection are common characteristics of both tumors. We report the specificity of surgical management, functional results and seizure outcome in cases of a tumor location in eloquent areas.

METHODS

Among 150 patients (88 males, 3-55 years) operated on for refractory epilepsy due to a glioneuronal tumor (1990-2015), 30 (20%, dysembryoplastic neuroepithelial tumors=21; gangliogliomas=9) had a tumor located in an eloquent cortex (sensory-motor, insular or language areas). Surgery was performed after a preoperative work-up, including stereo-electroencephalography in 48 patients (26%) and functional MRI in 100 (67%). MRI-guided lesionectomy was mainly performed in extra-temporal location, whereas an additional corticectomy was performed in a temporal location. Tumor microsurgical resections were guided using neuronavigation and cortical/subcortical electrical stimulations. Multiple stereotactic thermocoagulations were performed in two insular tumors.

RESULTS

New motor/language deficits related to eloquent areas occurred postoperatively in 6/30 patients (20%) without any major permanent disability. Minor sensorimotor (n=2) and moderate language disturbance (n=1) persisted in three of them. Postoperative seizure-free outcome (mean follow-up>5 years) was obtained in 81% of the entire series, but significantly decreased to 60% in eloquent areas. Incomplete tumor resection was the main cause of surgical failure. However, unfavorable seizure outcome was also observed despite complete tumor resection. Malignant transformation occurred in one ganglioglioma.

CONCLUSION

Epilepsy surgery for benign glioneuronal tumors in eloquent areas provides acceptable results regarding the functional risks. Complete tumor resection is crucial for long-term favorable outcome.

Roles of phosphoinositide-specific phospholipase Cγ1 in brain development

Over the past decade, converging evidence suggests that PLCγ1 signaling has key roles in controlling neural development steps. PLCγ1 functions as a signal transducer that converts an extracellular stimulus into intracellular signals by generating second messengers such as DAG and IP3. DAG functions as an activator of either PKC or transient receptor potential cation channels (TRPCs), while IP3 induces the calcium release from intracellular calcium stores. These second messengers regulate the morphological change of neuron, such as neurite outgrowth, migration, axon pathfinding, and synapse formation. These morphological changes depend on finely tuned calcium signaling following receptor tyrosine kinase-mediated PLCγ1 signaling. Thus, deregulation of PLCγ1 signaling causes various abnormalities of neuronal development and it may be associated with diverse neurological disorders. Herein, we discuss the current understanding of the PLCγ1 signaling pathway in neural development and provide recent advances of how PLCγ1 signaling is involved in the formation of neuronal processes for functionally faithful brain development.

Vestibular substitution: comparative study

OBJECTIVE

To determine the efficacy of vestibular rehabilitation with the electrotactile vestibular substitution system, as a new treatment modality in patients with bilateral vestibular disorders.

STUDY DESIGN AND SETTINGS

Nineteen patients with bilateral, chronic, idiopathic vestibulopathy were studied prospectively. Patients were divided to two groups. Patients in the first group were rehabilitated with the electrotactile vestibular substitution system, while patients in the second group were treated with standard vestibular rehabilitation therapy. The sensory organisation test and dizziness handicap inventory were used to compare the pre- and post-training results of both rehabilitative treatments.

RESULTS

All group one patients in the standardised testing subset demonstrated improved results for both the composite sensory organisation test and for the functional transfer aspect of the dizziness handicap inventory, after five days' training with the electrotactile vestibular substitution system. In contrast, group two patients showed no significant improvement in their composite sensory organisation test or dizziness handicap inventory scores after eight weeks of therapy, compared with pre-treatment levels.

CONCLUSION

These preliminary results indicate the efficacy of the electrotactile vestibular substitution system in improving patients' symptoms of vestibulopathy, and constitute evidence of successful sensory substitution.

Effects of electrotactile vestibular substitution on rehabilitation of patients with bilateral vestibular loss

The present study evaluated the effectiveness of electrotactile tongue biofeedback (BrainPort((R))) as a sensory substitute for the vestibular apparatus in patients with bilateral vestibular loss (BVL) who did not have a good response to conventional vestibular rehabilitation (VR). Seven patients with BVL were trained to use the device. Stimulation on the surface of the tongue was created by a dynamic pattern of electrical pulses and the patient was able to adjust the intensity of stimulation and spatially centralize the stimulus on the electrode array. Patients were directed to continuously adjust head orientation and to maintain the stimulus pattern at the center of the array. Postural tasks that present progressive difficulties were given during the use of the device. Pre- and post-treatment distribution of the sensory organization test (SOT) composite score showed an average value of 38.3+/-8.7 and 59.9+/-11.3, respectively, indicating a statistically significant improvement (p=0.01). Electrotactile tongue biofeedback significantly improved the postural control of the study group, even if they had not improved with conventional VR. The electrotactile tongue biofeedback system was able to supply additional information about head position with respect to gravitational vertical orientation in the absence of vestibular input, improving postural control. Patients with BVL can integrate electrotactile information in their postural control in order to improve stability after conventional VR. These results were obtained and verified not only by the subjective questionnaire but also by the SOT composite score. The limitations of the study are the small sample size and short duration of the follow-up. The current findings show that the sensory substitution mediated by electrotactile tongue biofeedback may contribute to the improved balance experienced by these patients compared to VR.

Understanding wiring and volume transmission

The proposal on the existence of two main modes of intercellular communication in the central nervous system (CNS) was introduced in 1986 and called wiring transmission (WT) and volume transmission (VT). The major criterion for this classification was the different characteristics of the communication channel with physical boundaries well delimited in the case of WT (axons and their synapses; gap junctions) but not in the case of VT (the extracellular fluid filled tortuous channels of the extracellular space and the cerebrospinal fluid filled ventricular space and sub-arachnoidal space). The basic dichotomic classification of intercellular communication in the brain is still considered valid, but recent evidence on the existence of unsuspected specialized structures for intercellular communication, such as microvesicles (exosomes and shedding vesicles) and tunnelling nanotubes, calls for a refinement of the original classification model. The proposed updating is based on criteria which are deduced not only from these new findings but also from concepts offered by informatics to classify the communication networks in the CNS. These criteria allowed the identification also of new sub-classes of WT and VT, namely the "tunnelling nanotube type of WT" and the "Roamer type of VT." In this novel type of VT microvesicles are safe vesicular carriers for targeted intercellular communication of proteins, mtDNA and RNA in the CNS flowing in the extracellular fluid along energy gradients to reach target cells. In the tunnelling nanotubes proteins, mtDNA and RNA can migrate as well as entire organelles such as mitochondria. Although the existence and the role of these new types of intercellular communication in the CNS are still a matter of investigation and remain to be fully demonstrated, the potential importance of these novel types of WT and VT for brain function in health and disease is discussed.

Vestibular rehabilitation with electrotactile vestibular substitution: early effects

We aimed to determine the early efficacy of vestibular rehabilitation with electrotactile vestibular substitution system (EVSS) as a new treatment modality in patients with bilateral vestibular loss due to aminoglycoside-induced ototoxicity. Six men and four women with bilateral vestibular failure were rehabilitated with EVSS prospectively. Patients were trained with EVSS for ten sessions each lasted 20 min, two sessions per day. Sensory organization test (SOT) protocol and dizziness handicap inventory (DHI) were used to compare pre- and post-training results of the rehabilitative treatment. Post-training tests were done at the first day of post-treatment period. All ten patients in the standardized testing subset demonstrated improved scores in the composite SOT scores and in the functional transfer testing with DHI after 5 days of training with the EVSS. In conclusion, these preliminary results demonstrate efficacy of the EVSS in improving patients symptoms and signs and signify the evidence of sensory substitution in the early post-training period.

[Surgical resections in functional areas: report of 89 cases]

Surgical resections for intractable epilepsy are generally associated with a high risk of permanent neurological deficit and a poor rate of seizure control. We present a series of 89 patients operated on from 1992 through 2007 for drug-resistant partial epilepsy, in whom surgery was performed in a functional area of the brain: the central (sensorimotor and supplementary motor areas) region in 48 cases, posterior regions (parietal and occipital) in 27, the insula in eight, and the language areas in six. Epilepsy was cryptogenic in 12 patients, and lesion-related in 77: malformation of cortical development in 43, tumor in 17, perinatal cicatrix in 13, vascular lesion in three, and another prenatal lesion in one. Seventy patients underwent stereoelectroencephalographic (SEEG) exploration. The surgical procedure was resective (lesionectomy or SEEG-guided corticectomy) in 83 patients and multiple stereotactic thermocoagulations in six. Ten patients were reoperated because of early seizure recurrence. A postoperative complication was observed in 12 patients. Postoperative deficits were observed in 54 patients (61%) and resolved completely in 29. In 25, a permanent deficit persisted, minor in 19 and moderate to severe in six, which did not correlate with localization or etiology. With a one-year follow-up in 74 patients (mean, 3.6 years), 53 (72%) were in Engel's class I, including 38 (51%) in class IA. Seizure outcome was significantly associated with etiology: 93% of Taylor-type focal cortical dysplasia, whereas only 40% of cryptogenic epilepsies were in class I (p<0.05). This suggests that resective or disconnective surgery for intractable partial epilepsy in functional areas of the brain may be followed by excellent results on seizures and a moderate risk of permanent neurological sequelae.

Efficacy of electrotactile vestibular substitution in patients with bilateral vestibular and central balance loss

Patients with bilateral vestibular loss (BVL) of both central and peripheral origin experience multiple problems with balance and posture control, movement, and abnormal gait.Wicab, Inc. has developed the BrainPort balance device to transmit head position/orientation information normally provided by the vestibular system to the brain through a substitute sensory channel: electrotactile stimulation of the tongue. Head-orientation data (artificially sensed) serves as the input signal for the BrainPort balance device to control the movement of a small pattern of stimulation on the tongue that relates to head position in real-time. With training, the brain learns to appropriately interpret the information from the device and utilize it to function as it would with data from a normal-functioning natural sense. Ina total of 40 subjects trained with the BrainPort, 18 have been tested using standardized quantitative measurements of the treatment effects. A specialized set of exercises, testing, and training procedures has been developed that may serve as the course of intensive physical therapy with the BrainPort balance device. Our results demonstrate consistent positive and statistically significant balance rehabilitation effects independent of aging and etiology of balance deficit.

Behavioral functions of the mesolimbic dopaminergic system: an affective neuroethological perspective

The mesolimbic dopaminergic (ML-DA) system has been recognized for its central role in motivated behaviors, various types of reward, and, more recently, in cognitive processes. Functional theories have emphasized DA's involvement in the orchestration of goal-directed behaviors and in the promotion and reinforcement of learning. The affective neuroethological perspective presented here views the ML-DA system in terms of its ability to activate an instinctual emotional appetitive state (SEEKING) evolved to induce organisms to search for all varieties of life-supporting stimuli and to avoid harms. A description of the anatomical framework in which the ML system is embedded is followed by the argument that the SEEKING disposition emerges through functional integration of ventral basal ganglia (BG) into thalamocortical activities. Filtering cortical and limbic input that spreads into BG, DA transmission promotes the "release" of neural activity patterns that induce active SEEKING behaviors when expressed at the motor level. Reverberation of these patterns constitutes a neurodynamic process for the inclusion of cognitive and perceptual representations within the extended networks of the SEEKING urge. In this way, the SEEKING disposition influences attention, incentive salience, associative learning, and anticipatory predictions. In our view, the rewarding properties of drugs of abuse are, in part, caused by the activation of the SEEKING disposition, ranging from appetitive drive to persistent craving depending on the intensity of the affect. The implications of such a view for understanding addiction are considered, with particular emphasis on factors predisposing individuals to develop compulsive drug seeking behaviors.

Neurotransmitter receptor heteromers and their integrative role in 'local modules': the striatal spine module

'Local module' is a fundamental functional unit of the central nervous system that can be defined as the minimal portion of one or more neurons and/or one or more glial cells that operates as an independent integrative unit. This review focuses on the importance of neurotransmitter receptor heteromers for the operation of local modules. To illustrate this, we use the striatal spine module (SSM), comprised of the dendritic spine of the medium spiny neuron (MSN), its glutamatergic and dopaminergic terminals and astroglial processes. The SSM is found in the striatum, and although aspects such as neurotransmitters and receptors will be specific to the SSM, some general principles should apply to any local module in the brain. The analysis of some of the receptor heteromers in the SSM shows that receptor heteromerization is associated with particular elaborated functions in this local module. Adenosine A(2A) receptor-dopamine D(2) receptor-glutamate metabotropic mGlu(5) receptor heteromers are located adjacent to the glutamatergic synapse of the dendritic spine of the enkephalin MSN, and their cross-talk within the receptor heteromers helps to modulate postsynaptic plastic changes at the glutamatergic synapse. A(1) receptor-A(2A) receptor heteromers are found in the glutamatergic terminals and the molecular cross-talk between the two receptors in the heteromer helps to modulate glutamate release. Finally, dopamine D(2) receptor-non-alpha(7) nicotinic acetylcholine receptor heteromers, which are located in dopaminergic terminals, introduce the new concept of autoreceptor heteromer.

fMRI MODELS OF DENDRITIC AND ASTROCYTIC NETWORKS

In order to elucidate the relationships between hierarchical structures within the neocortical neuropil and the information carried by an ensemble of neurons encompassing a single voxel, it is essential to predict through volume conductor modeling LFPs representing average extracellular potentials, which are expressed in terms of interstitial potentials of individual cells in networks of gap-junctionally connected astrocytes and synaptically connected neurons. These relationships have been provided and can then be used to investigate how the underlying neuronal population activity can be inferred from the measurement of the BOLD signal through electrovascular coupling mechanisms across the blood-brain barrier. The importance of both synaptic and extrasynaptic transmission as the basis of electrophysiological indices triggering vascular responses between dendritic and astrocytic networks, and sequential configurations of firing patterns in composite neural networks is emphasized. The purpose of this review is to show how fMRI data may be used to draw conclusions about the information transmitted by individual neurons in populations generating the BOLD signal.

Volume transmission and wiring transmission from cellular to molecular networks: history and perspectives

The present paper deals with a fundamental issue in neuroscience: the inter-neuronal communication. The paper gives a brief account of our previous and more recent theoretical contributions to the subject and also reports new recent data that support some aspects of our proposal on two major modes of communication in the central nervous system: the wiring and the volume transmission. There exist two competing theories on inter-neuronal communication: the neuron doctrine and the theory of the diffuse nerve network, supported by Cajal and Golgi, respectively (see their respective Nobel Lectures). The present paper gives a brief account of a view on inter-neuronal communication in the brain, the volume and wiring transmission concept that to a great extent reconcile these two theories. Thus, the theory of volume and wiring transmission are summarized and its recent developments that allow to extend these two modes of communication from the cellular network to the molecular network level is also briefly illustrated. The explanatory value of this broadened view is further enhanced by our recent proposal on the existence of a Global Molecular Network enmeshing the entire central nervous system. It may be interesting to note that also the Global Molecular Network theory is reminiscent of the old reticular theory of Apathy. Finally, the so-called 'tide hypothesis' for diffusion of signals in the brain is briefly discussed and its possible extension to the molecular level is for the first time introduced. Early indirect evidence supporting volume transmission in the brain was the discovery of transmitter-receptor mismatches. Thus, as an experimental part of the present paper a new approach to evaluate transmitter-receptor mismatches is given and evidence for inter-relationships between temperature micro-gradients and mismatches is provided.

SOME RADICAL IMPLICATIONS OF BACH-Y-RITA'S DISCOVERIES

Bach-y-Rita's clinical results in restoring lost sensory function are based on several phenomena not widely appreciated in cognitive science. First, there is volume transmission. Extensive laboratory observation has shown that the brain is much more than a network of synaptically connected neurons. Bach-y-Rita has found that a key implication of volume transmission is that it is a functional component in adult brain plasticity, also widely observed experimentally. Plasticity has led him to conclude that the structure of brain dynamics is beyond the scope of algorithmic computation. If the brain is not a computer, this insight would have a significant impact on the development of new technologies based on brain function. Bach-y-Rita's work is being extended from restoration of lost senses to the creation of new senses. This in turn could lead to a new technology of "wiring a human-in-the-loop" that would be utterly unlike any computationally based technology. Instead of mere interaction with a machine, the human "becomes one" with it.

THERE IS SOMETHING OUT THERE: DISTAL ATTRIBUTION IN SENSORY SUBSTITUTION, TWENTY YEARS LATER

Sensory substitution constitutes an interesting domain of study to consider the philosopher's classical question of distal attribution: how we can distinguish between a sensation and the perception of an object that causes this sensation. We tested the hypothesis that distal attribution consists of three distinct components: an object, a perceptual space, and a coupling between subjects' movements and stimulation. We equipped sixty participants with a visual-to-auditory substitution device, without any information about it. The device converts the video stream produced by a head-mounted camera into a sound stream. We investigated several experimental conditions: the existence or not of a correlation between movements and resulting stimulation, the direct or indirect manipulation of an object, and the presence of a background environment. Participants were asked to describe their impressions by rating their experiences in terms of seven possible "scenarios". These scenarios were carefully chosen to distinguish the degree to which the participants attributed their sensations to a distal cause. Participants rated the scenarios both before and after they were given the possibility to interrupt the stimulation with an obstacle. We were interested in several questions. Did participants extract laws of co-variation between their movements and resulting stimulation? Did they deduce the existence of a perceptual space originating from this coupling? Did they individuate objects that caused the sensations? Whatever the experimental conditions, participants were able to establish that there was a link between their movements and the resulting auditory stimulation. Detection of the existence of a coupling was more frequent than the inferences of distal space and object.