Galina Kataeva

Comparison of brain activation after sustained non-fatiguing and fatiguing muscle contraction: a positron emission tomography study

The concept of fatigue refers to a class of acute effects that can impair motor performance, and not to a single mechanism. A great deal is known about the peripheral mechanisms underlying the process of fatigue, but our knowledge of the roles of the central structures in that process is still very limited. During fatigue, it has been shown that peripheral apparatus is capable of generating adequate force while central structures become insufficient/sub-optimal in driving them. This is known as central fatigue, and it can vary between muscles and different tasks. Fatigue induced by submaximal isometric contraction may have a greater central component than fatigue induced by prolonged maximal efforts. We studied the changes in regional cerebral blood flow (rCBF) of brain structures after sustained isometric muscle contractions of different submaximal force levels and of different durations, and compared them with the conditions observed when the sustained muscle contraction becomes fatiguing. Changes in cortical activity, as indicated by changes in rCBF, were measured using positron emission tomography (PET). Twelve subjects were studied under four conditions: (1) rest condition; (2) contraction of the m. biceps brachii at 30% of MVC, sustained for 60 s; (3) contraction at 30% of MVC, sustained for 120 s, and; (4) contraction at 50% of MVC, sustained for 120 s. The level of rCBF in the activated cortical areas gradually increased with the level and duration of muscle contraction. The fatiguing condition was associated with predominantly contralateral activation of the primary motor (MI) and the primary and secondary somatosensory areas (SI and SII), the somatosensory association area (SAA), and the temporal areas AA and AI. The supplementary motor area (SMA) and the cingula were activated bilaterally. The results show increased cortical activation, confirming that increased effort aimed at maintaining force in muscle fatigue is associated with increased activation of cortical neurons. At the same time, the activation spread to several cortical areas and probably reflects changes in both excitatory and inhibitory cortical circuits. It is suggested that further studies aimed at controlling afferent input from the muscle during fatigue may allow a more precise examination of the roles of each particular region involved in the processing of muscle fatigue.

An ER-fMRI study of Russian inflectional morphology

The generation of regular and irregular past tense verbs has long been a testing ground for different models of inflection in the mental lexicon. Behavioral studies examined a variety of languages, but neuroimaging studies rely almost exclusively on English and German data. In our fMRI experiment, participants inflected Russian verbs and nouns of different types and corresponding nonce stimuli. Irregular real and nonce verbs activated inferior frontal and inferior parietal regions more than regular verbs did, while no areas were more activated in the opposite comparison. We explain this activation pattern by increasing processing load: a parametric contrast revealed that these regions are also more activated for nonce stimuli compared to real stimuli. A very similar pattern is found for nouns. Unlike most previously obtained results, our findings are more readily compatible with the single-system approach to inflection, which does not postulate a categorical difference between regular and irregular forms.

Changes of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in the model of experimental acute hydrocephalus in rabbits

BackgroundTo study the integrity of white matter, we investigated the correlation between the changes in neuroradiological and morphological parameters in an animal model of acute obstructive hydrocephalus.MethodsHydrocephalus was induced in New Zealand rabbits (n = 10) by stereotactic injection of kaolin into the lateral ventricles. Control animals received saline in place of kaolin (n = 10). The progression of hydrocephalus was assessed using magnetic resonance imaging. Regional fractional anisotropy (FA) and the apparent diffusion coefficient (ADC) were measured in several white matter regions before and after the infusion of kaolin. Morphology of myelinated nerve fibers as well as of the blood–brain barrier were studied with the help of transmission electron microscopy (TEM) and light microscopy.ResultsCompared with control animals, kaolin injection into the ventricles resulted in a dramatic increase in ventricular volume with compression of basal cisterns, brain shift and periventricular edema (as observed on magnetic resonance imaging [MRI]). The values of ADC in the periventricular and periaqueductal areas significantly increased in the experimental group (P < 0.05). FA decreased by a factor of 2 in the zones of periventricular, periaqueductal white matter and corpus collosum. Histological analysis demonstrated the impairment of the white matter and necrobiotic changes in the cortex. Microsctructural alterations of the myelin fibers were further proved with the help of TEM. Blood–brain barrier ultrastructure assessment showed the loss of its integrity.ConclusionsThe study demonstrated the correlation of the neuroradiological parameters with morphological changes. The abnormality of the FA and ADC parameters in the obstructive hydrocephalus represents a significant implication for the diagnostics and management of hydrocephalus in patients.

Factor Structure of Regional Cerebral Blood Flow and Glucose Metabolism Rate as a Tool to Study the Default Mode of the Brain

The functional connectivity of anatomical and functional brain structures in the state of operational rest was assessed on the basis of positron emission tomography (PET) data to study the so-called default mode of the brain, i.e., the brain’s spontaneous activity at rest.It is concluded that the possibility of identifying neuroanatomical systems of the default mode (default mode network) in routine clinical PET studies of the cerebral blood flow and glucose metabolism is important for studying the functional organization of the brain in the normal state and its rearrangements in pathologies.

Polyfunctionality of neurons: The blocking of extreme pathological afferentation leads to an improvement of the higher functions of the brain

In this paper, a possible mechanism for improving the functional state of the brain regions maintaining locomotor, visual, auditory, and higher functions of the brain during the correction of the generalized spastic syndrome (botulinotherapy with Xeomin) in patients in the vegetative state (VS) is discussed. If the vegetative state is considered as a stable pathological condition (SPC) of the brain, then, in terms of the theory of the structural-functional organization of brain systems with rigid and flexible elements (N.P. Bechtereva), the therapy led to an unbalance of SPC, functional liberation of neurons, redistribution of their functions to ensure other activities, and the formation of new interneuronal connections. Taking into account the functional variability of neurons (S.V. Medvedev), the blocking of the neuromuscular transmission in spastic muscles reduces the abnormal afferent and efferent hyperactivity of motor and sensory neuronal circuits, which liberates the brain for other activities. Clinically, this allows considering botulinotherapy of drug-resistant muscle spasticity in patients in VS and minimal consciousness not only as a symptomatic treatment but also as indirect neuroprotection.

Functional activity of brain structures and predisposition to aggression in patients with lingering diseases of the CNS

The relationships of unconscious aggression (according to the Hand Test) with regional glucose metabolic rates in the brain (estimated using positron emission tomography) have been analyzed in patients with multiple sclerosis. It has been shown that an increased proneness to open aggression (unconscious aggression) in patients with multiple sclerosis is mainly related to reduced functioning of different areas of the frontal lobes of the brain on the left and with changes in glucose metabolic rate in the structures of the limbic system of the left and right hemispheres. An enhanced unconscious aggression is accompanied by a decrease in the glucose metabolic rate in some areas of Broca’s convolution and the middle frontal gyrus on the left.