מחקרים נבחרים

 

 

Is realistic neuronal modeling realistic?

Almog, M., Korngreen, A.

August 2016 | Journal of Neurophysiology

 

Scientific models are abstractions that aim to explain natural phenomena. A successful model shows how a complex phenomenon arises from relatively simple principles while preserving major physical or biological rules and predicting novel experiments. A model should not be a facsimile of reality; it is an aid for understanding it. Contrary to this basic premise, with the 21st century has come a surge in computational efforts to model biological processes in great detail. Here we discuss the, oxymoronic, realistic modeling of single neurons. This rapidly advancing field is driven by the discovery that some neurons don't merely sum their inputs and fire if the sum exceeds some threshold. Thus, researchers have asked what are the computational abilities of single neurons, and attempted to give answers using realistic models. We briefly review the state of the art of compartmental modeling highlighting recent progress and intrinsic flaws. We then attempt to address two fundamental questions. Practically, can we realistically model single neurons? Philosophically, should we realistically model single neurons? We use layer 5 neocortical pyramidal neurons as a test case to examine these issues. We subject three publically available models of layer 5 pyramidal neurons to three simple computational challenges. Based on their performance and a partial survey of published models, we conclude that current compartmental models are ad hoc, unrealistic models functioning poorly once they are stretched beyond the specific problems for which they were designed. We then attempt to plot possible paths for generating realistic single neuron models.

 

 

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מחקרים נבחרים - ארכיון

 

Exploring the unconscious using faces

Axelrod, V., M. Bar and Rees, G.

January 2015 | Trends in Cognitive Studies

 

Understanding the mechanisms of unconscious processing is one of the most substantial endeavors of cognitive science. While there are many different empirical ways to address this question, the use of faces in such research has proven exceptionally fruitful. We review here what has been learned about unconscious processing through the use of faces and face-selective neural correlates. A large number of cognitive systems can be explored with faces, including emotions, social cueing and evaluation, attention, multisensory integration, and various aspects of face processing.

 

 

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Beyond words: evidence for automatic language–gesture integration of symbolic gestures but not dynamic landscapes

Vainiger, D., L. Labruna, R. B. Ivry and M. Lavidor

January 2014 | Psychological research

 

Understanding actions based on either language or action observation is presumed to involve the motor system, reflecting the engagement of an embodied conceptual network. We examined how linguistic and gestural information were integrated in a series of cross-domain priming studies. We varied the task demands across three experiments in which symbolic gestures served as primes for verbal targets. Primes were clips of symbolic gestures taken from a rich set of emblems. Participants responded by making a lexical decision to the target (Experiment 1), naming the target (Experiment 2), or performing a semantic relatedness-judgment (Experiment 3). The magnitude of semantic priming was larger in the relatedness-judgment and lexical decision tasks compared to the naming task. Priming was also observed in a control task in which the primes were pictures of landscapes with conceptually related verbal targets. However, for these stimuli, the amount of priming was similar across the three tasks. We propose that action observation triggers an automatic, pre-lexical spread of activation, consistent with the idea that language-gesture integration occurs in an obligatory and automatic fashion.

 

 

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Mindfulness-induced selflessness: A MEG neurophenomenological study

Dor-Ziderman, Y., A. Berkovich-Ohana, J. Glicksohn and A. Goldstein

September 2013 | Frontiers in Human Neuroscience

 

Contemporary philosophical and neurocognitive studies of the self have dissociated two distinct types of self-awareness: a “narrative” self-awareness (NS) weaving together episodic memory, future planning and self-evaluation into a coherent self-narrative and identity, and a “minimal” self-awareness (MS) focused on present momentary experience and closely tied to the sense of agency and ownership. Long-term Buddhist meditation practice aims at realization of a “selfless” mode of awareness (SL), where identification with a static sense of self is replaced by identification with the phenomenon of experiencing itself. NS-mediating mechanisms have been explored by neuroimaging, mainly fMRI, implicating prefrontal midline structures, but MS processes are not well characterized and SL even less so. To this end we tested 12 long-term mindfulness meditators using a neurophenomenological study design, incorporating both magnetoencephalogram (MEG) recordings and first person descriptions. We found that (1) NS attenuation involves extensive frontal, and medial prefrontal gamma band (60–80 Hz) power decreases, consistent with fMRI and intracranial EEG findings; (2) MS attenuation is related to beta-band (13–25 Hz) power decreases in a network that includes ventral medial prefrontal, medial posterior and lateral parietal regions; and (3) the experience of selflessness is linked to attenuation of beta-band activity in the right inferior parietal lobule. These results highlight the role of dissociable frequency-dependent networks in supporting different modes of self-processing, and the utility of combining phenomenology, mindfulness training and electrophysiological neuroimaging for characterizing self-awareness.

 

 

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Population Responses to Contour Integration: Early Encoding of Discrete Elements and Late Perceptual Grouping

Ariel Gilad, Elhanan Meirovithz and Hamutal Slovin

April 2013 | Neuron

 

The neuronal mechanisms underlying perceptual grouping of discrete, similarly oriented elements are not well understood. To investigate this, we measured neural population responses using voltage-sensitive dye imaging in V1 of monkeys trained on a contour-detection task. By mapping the contour and background elements onto V1, we could study their neural processing. Population response early in time showed activation patches corresponding to the contour/background individual elements. However, late increased activity in the contour elements, along with suppressed activity in the background elements, enabled us to visualize in single trials a salient continuous contour popping out from a suppressed background. This modulated activity in the contour and in background extended beyond the cortical representation of individual contour or background elements. Finally, the late modulation was correlated with behavioral performance of contour saliency and the monkeys perceptual report. Thus, opposing responses in the contour and background may underlie perceptual grouping in V1.

 

 

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Auditory abstraction from spectro-temporal features to coding auditory entities

Gal Chechik and Israel Nelken

October 2012 | Proceedings of the National Academy of Sciences

 

The auditory system extracts behaviorally relevant information from acoustic stimuli. The average activity in auditory cortex is known to be sensitive to spectro-temporal patterns in sounds. However, it is not known if the auditory cortex also processes more abstract features of sounds, which may be more behaviorally relevant than spectro-temporal patterns. Chechik and Nelken recorded from three stations of the cat auditory pathway in response to natural sounds: the inferior colliculus (IC), the medial geniculate body (MGB) of the thalamus, and the primary auditory cortex (A1). They compared the information that spikes contained about two aspects of the stimuli: spectro-temporal patterns, and abstract entities present in the same stimuli such as a bird chirp, its echoes, and the ambient noise.

 

IC spikes conveyed on average approximately the same amount of information about spectro-temporal patterns as they conveyed about abstract auditory entities, but A1 and the MGB neurons conveyed on average three times more information about abstract auditory entities than about spectro-temporal patterns. Thus, the neurons in auditory thalamus and cortex coded well the presence of abstract entities in the sounds without coding well their spectro-temporal structure. This suggests that they are sensitive to abstract features in these sounds.

 

 

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Genetic Ablation of Hypocretin Neurons Alters Behavioral State Transitions in Zebrafish

Idan Elbaz, Laura Yelin-Bekerman, Julian Nicenboim, Gad Vatine and Lior Appelbaum

September 2012 | The Journal of Neuroscience

 

Sleep is an essential biological need of all animals studied to date. The sleep disorder narcolepsy is characterized by excessive daytime sleepiness, fragmentation of nighttime sleep, and cataplexy. Narcolepsy is caused by selective degeneration of hypothalamic hypocretin/orexin (HCRT) neurons. In mammals, HCRT neurons primarily regulate the sleep/wake cycle, feeding, reward-seeking, and addiction. The role of HCRT neurons in zebrafish is implicated in both sleep and wake regulation. We established a transgenic zebrafish model enabling inducible ablation of HCRT neurons and used these animals to understand the function of HCRT neurons and narcolepsy. Loss of HCRT neurons increased the expression of the HCRT receptor (hcrtr). Behavioral assays revealed that HCRT neuron-ablated larvae had normal locomotor activity, but demonstrated an increase in sleep time during the day and an increased number of sleep/wake transitions during both day and night. Mild sleep disturbance reduced sleep and increased c-fos expression in HCRT neuron-ablated larvae. Furthermore, ablation of HCRT neurons altered the behavioral response to external stimuli. Exposure to light during the night decreased locomotor activity of wild-type siblings, but induced an opposite response in HCRT neuron-ablated larvae. Sound stimulus during the day reduced the locomotor activity of wild-type sibling larvae, while HCRT neuron-ablated larvae demonstrated a hyposensitive response. This study establishes zebrafish as a model for narcolepsy, and indicating a role of HCRT neurons in regulation of sleep/wake transitions during both day and night. Our results further suggest a key role of HCRT neurons in mediating behavioral state transitions in response to external stimuli.

 

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The neurobiology of falls

Alfonso Fasano, Meir Plotnik, Francesco Bove and Alfredo Berardelli

June 2012 | Neurological sciences

 

Falling is a major clinical problem; especially, in elderly population as it often leads to fractures, immobilization, poor quality of life and life-span reduction. Given the growing body of evidences on the physiopathology of balance disorders in humans, in recent years the approach of research on falls has completely changed and new instruments and new definitions have been formulated. Among them, the definition of "idiopathic faller" (i.e. no overt cause for falling in a given subject) represented a milestone in building the "science of falling". This review deals with the new determinants of the neurobiology of falling: (1) the role of motor impairment and particularly of those "mild parkinsonian signs" frequently detectable in elderly subjects, (2) the role of executive and attentive resources when coping with obstacles, (3) the role of vascular lesions in "highest level gait disorder" (a condition tightly connected with senile gait, cautious gait and frailty), (4) the role of the failure of automaticity or inter-limbs coordination/symmetry during walking and such approach would definitely help the development of screening instrument for subjects at risk (still lacking in present days). This translational approach will lead to the development of specific therapeutic interventions.

 

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Magnocellular training of word recognition

Tara Chouake, Tamar Levy, Daniel C. Javitt and Michal Lavidor

February 2012 | Frontiers in Human Neuroscience

 

Current research has shown that basic visual networks, such as the magnocellular system, may play a crucial role in reading deficits related to dyslexia. This study, led by Michal Lavidor, explored the relationship between magnocellular activity and reading abilities, and tested the hypothesis that a repeated usage of the magnocellular stream may improve reading by strengthening crucial neural pathways. Visual training was conducted for five consecutive days using a motion detection task (magnocellular training) and a control task of pattern detection (parvocellular training). Reading abilities of skilled readers were measured before and after the training using a lexical decision task. The group found that low-grade visual training overall can improve speed of lexical decision, but there is some indication that magnocellular training may selectively relate to accuracy. This potential added benefit of accuracy is crucial, and indicates that magnocellular training may have an advantage to parvocellular or general visual training when it comes to reading. This result lends support to the role of basic visual systems in reading, and has potential implications for neurorehabilitation of reading-related deficits.

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Neuropsychological assessment: principles, rationale, and challenges

Eli Vakil

November 2011 | Journal of Clinical and Experimental Neuropsychology

 

Neuropsychological assessments are increasingly in demand for a wide range of patients. This paper, by Eli Vakil, offers a survey of the basic aspects of neuropsychological assessment that are of greatest importance for professionals (e.g., psychologists, psychiatrists, social workers, and lawyers) who are not trained in neuropsychological testing, but who refer clients for neuropsychological assessment. This survey could also serve neuropsychologists in their early stages of training, by addressing some of the major issues related to the assessment process.

 

The paper presents a model that explains the rationale enabling generalization from assessment to real-world functions that are the focus of interest and the target of prediction. Issues that need to be considered before deciding to conduct a neuropsychological evaluation are introduced, and sources of information available to the assessor are described. A description is provided of what a neuropsychological assessment includes, with an emphasis on its cognitive aspects. Finally, mention is made of some of the difficulties and challenges that must be confronted in the course of a neuropsychological assessment.

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Activation of the Right Hemisphere Using Muscle Contractoin Improves Creativity

Abraham Goldstein, Ketty Revivo, Michal Kreitler and Nili Metuki

2010 | Psychonomic Bulletin & Review

 

A study conducted by Dr. Avi Goldstein and colleagues shows that artificially activating the right hemisphere ahead of time using a task as simple as squeezing a ball enhances creativity.

In this study, published last year, participants squeezed balls with their left hand (thus activating the right hemisphere) or the right hand (which activates the left hemisphere). The participants were then given a task that measures creative problem solving.

 

A widely held notion is that the information-processing style used by the right hemisphere facilitates creative thinking. The researchers hypothesized that left-hand contractions would cause right hemisphere activation, shifting the hemispheric asymmetry and leading to better scores in the creative thinking task, which was indeed the case. This simple technique is therefore potentially therapeutic, and could have wide applications in aiding individuals with language impairments or other disorders that are believed to be related to hemispheric imbalances.

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Investigating the Neural Origins of Motor Tics

Maya Bronfeld, Katya Belelovsky and Izhar Bar-Gad

June 2011 | The Journal of Neuroscience

 

Motor tics are brief, involuntary muscle contractions that occur in several neurological conditions. Tics are probably produced by abnormal activity in circuits involving cortex and basal ganglia, but their site of origin remains controversial. To address this question, Maya Bronfeld and Katya Belelovsky, under the supervision of Dr. Izhar Bar-Gad, induced orofacial tics in primates by injecting GABA antagonist into the dorsal putamen, the input structure of the basal ganglia, and recording activity in other areas. Tic related bursting occurred in presumptive medium spiny neurons (MSNs) in the ventral putamen, and activity modulation was recorded throughout the globus pallidus externus (GPe), GP internus (GPi) (the main motor output nucleus of the basal ganglia), and in primary motor cortex (M1). Tic-related activity in presumptive MSNs generally preceded modulations in M1, which usually preceded those in GPe and GPi. The relative timing and lack of regional specificity of pallidal modulation suggests that, contrary to some models, GPi does not initiate tics or determine which muscles they involve.