The main directions of the group:
Spatio-temporal dynamics of the neuronal activity
In this project we plan to study the spatial and temporal patterns of the neuronal activity of the human brain during various tasks (sensory, motor or cognitive), as well as at rest state. Particular attention will be paid on the possibility of describing the neuronal processes as a complex system, using, for example, the hypothesis of the existence of a critical brain state which may be optimal for the neuronal networks functioning. In this regard the use of long-range temporal correlations (LRTC), which existence we showed earlier in the temporal dynamics of amplitude envelope of neuronal oscillations, may be interesting. We are going to assess synchronization and causal interactions for description of processes of neuronal interactions. For a complete description of neuronal processes it is reasonable to study both spontaneous and evoked neuronal activity, as well as possible interactions between them.
Especially interesting in this regard is the identification of the relationship between spontaneous / resting component of the neuronal activity and subsequent behavioral responses and evoked activity. This approach allows to study human brain reactions in the context of neuronal state. We are going to study the distributed spatial neuronal processes using multi-channel EEG, a method with high time resolution (milliseconds). For a more precise space-time description of the EEG, we are going to develop algorithms based on the analysis of multidimensional data. We are also going to use MRI-navigated transcranial magnetic stimulation (nTMS) and nTMS combined with EEG for testing and changing of the current neuronal state.
Study of convergence of descending and ascending systems of the brain
It is well known that descending and ascending brain systems have a clear hierarchical structural and functional organization, and that they are interacting with each other at different levels (sensorimotor coordination). We are going to study these systems non-invasively using TMS. For this purpose it is possible to use such phenomena of neuronal systems functioning as temporal and spatial summation. It is known that the neural response at the stimulation depends on the synchronization of the activating stimuli arrival. Therefore studying the correlation between the activating stimulus and the magnitude of the response allows to judge about the place of convergence in the neural network (spatial summation).
Using two synchronized magnetic stimulators allows us to stimulate two diffrent brain regions simulataneously or within concrete time period of several milliseconds (as well as to combine central and peripheral stimulation) while simultaneous registration of the perifereal responses, for example in a form of electromiogram (EMG) and/or central responses in a form of electroencephalogram (EEG). TMS is useful for stimulation not only of the cortical areas, but also of the spinal cord and peripheral nervous system (e.g., primary afferents). Estimation of the latent periods of the early components of the EMG allows to study the minimum number of synapses in the tested pathways. It is also possible to explore the early components of the evoked response (ERP) during the stimulation of somatosensory afferents. Thus, this approah allows to revise the structure of human neural networks, and to compare them with the results received in acute electrophysiological experiments on animals.
As an example it is possible to list the following problems:
- Studying of the phenomenon of convergence of contra- and ipsilateral corticospinal tract at the same neurons of the spinal cord
- Identification of the propriospinal system in the human spinal cord (corticospinal tract stimulation and primary afferents stimulation, with EMG recording)
- Investigation of the components of somatosensory ERP using simultaneous stimulation of the different ascending pathways (which allows to evaluate the role of interneurons of the spinal cord for the generation of early ERP components)
- Assess of the activity of individual motor units at the resonse at TMS using needle electrodes
Stability assessment of sensory and motor maps of the brain
It is well known that the primary somatosensory and motor cortex has topographical organization. Such functional organization is a good example of the nervous system fundamental property - "spatial information encoding." It is still widely believed that this encoding should have a relatively rigid framework, which means for example an invariant link with a real physical stimulus (for somatosensory "homunculus") or a specific muscle (for motor "homunculus"). Picture of such motor and sensory homunculi is still essential for most neuroscience textbooks. However, in a number of studies (both in animals and in humans), it was shown that such sensory and motor maps are very variable. And they can vary not only from one experiment to another, but also in a very short period of time. It has been shown that the dominant system can change the receptive fields of the neurons almost immediately.
Therefore, it raises a question, what does it mean a "spontaneous" brain activity? The activity of "modulating brain systems" (eg, hypothalamus, limbic system, etc.) may reflect at the fact that the neuron can "start reacting" at the previously indifferent stimulus, thus its receptive field changes. This question remais open and our laboratory equipment allows to carry research in this fiels. MRI navigated TMS allows to study motor (based on EMG) and somatosensory cortical topographic maps. Somatosensory cortical TMS mapping can be performed by stimulating various primary afferents and simultaneous multi-channel multi-channel EEG recording of the ERPs. Studying of the pre- and post-stimulus EEG for each individual stimulus is a way for studying the role of spontaneous activity for the response.
As an example it is possible to list the following problems:
- Mapping of primary somatosensory and motor cortex
- Evaluation of temporal stability of somatosensory and motor cortical maps
- Evaluation of the stability of these maps depending on the task, emotional state and on the spontaneous brain activity
Vadim Nikulin, PhD
Maria Nazarova, MD/PhD
Research Fellow, Research project: Physiological and Cognitive Aspects of Long-range Temporal Correlations in Neuronal Oscillations
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