Alexander Korotkov

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.

Brain processing of tonic muscle pain induced by infusion of hypertonic saline

Most of the previous studies on the effects of pain on Regional Cerebral Blood Flow (rCBF) had been done with brief cutaneous or intramuscular painful stimuli. The aim of the present study was to investigate the effect on rCBF of long lasting tonic experimental muscle pain. To this end we performed PET investigations of rCBF following tonic experimental low back pain induced by continuous intramuscular infusion of hypertonic (5%) saline (HS) with computer controlled infusion pump into the right erector spinae on L3 level in 19 healthy volunteers. Changes in rCBF were measured with the use of 15O labelled water during four conditions: Baseline (before start of infusion), Early Pain (4 min after start of infusion), Late Pain (20 min after start of infusion) and Post‐Pain (>15 min after stop of infusion) conditions.

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 in functional connectivity within the fronto-temporal brain network induced by regular and irregular Russian verb production

Functional connectivity between brain areas involved in the processing of complex language forms remains largely unexplored. Contributing to the debate about neural mechanisms underlying regular and irregular inflectional morphology processing in the mental lexicon, we conducted an fMRI experiment in which participants generated forms from different types of Russian verbs and nouns as well as from nonce stimuli. The data were subjected to a whole brain voxel-wise analysis of context dependent changes in functional connectivity [the so-called psychophysiological interaction (PPI) analysis]. Unlike previously reported subtractive results that reveal functional segregation between brain areas, PPI provides complementary information showing how these areas are functionally integrated in a particular task. To date, PPI evidence on inflectional morphology has been scarce and only available for inflectionally impoverished English verbs in a same-different judgment task. Using PPI here in conjunction with a production task in an inflectionally rich language, we found that functional connectivity between the left inferior frontal gyrus (LIFG) and bilateral superior temporal gyri (STG) was significantly greater for regular real verbs than for irregular ones. Furthermore, we observed a significant positive covariance between the number of mistakes in irregular real verb trials and the increase in functional connectivity between the LIFG and the right anterior cingulate cortex in these trails, as compared to regular ones. Our results therefore allow for dissociation between regularity and processing difficulty effects. These results, on the one hand, shed new light on the functional interplay within the LIFG-bilateral STG language-related network and, on the other hand, call for partial reconsideration of some of the previous findings while stressing the role of functional temporo-frontal connectivity in complex morphological processes.

Functional magnetic resonance study of deliberate deception

The goal of the study was analysis of the cerebral mechanisms of deliberate deception. The eventrelated functional magnetic resonance (ER fMRI) imaging technique was used to assess the changes in the functional brain activity by means of recording the blood oxygen level-dependent (BOLD) signal. Twelve right-handed healthy volunteers aged 19–44 years participated in the study. The BOLD images were obtained during three experimental trials: deliberate deception, manipulative honest and control truthful trials (catch trials). The deliberate deception and manipulative honest actions were characterized by a BOLD signal increase in the anterior cingulate (Brodmann’s area (BA) 32), frontal (BAs 9/10, 6), and parietal (BA 40) cortices as compared with a truthful response. Comparison of the ER fMRI data with the results of earlier studies where event-related potentials (ERPs) were recorded under similar conditions indicates the involvement of the brain mechanism of error detection in deliberate deception.

Deceptive but Not Honest Manipulative Actions Are Associated with Increased Interaction between Middle and Inferior Frontal gyri

The prefrontal cortex is believed to be responsible for execution of deceptive behavior and its involvement is associated with greater cognitive efforts. It is also generally assumed that deception is associated with the inhibition of default honest actions. However, the precise neurophysiological mechanisms underlying this process remain largely unknown. The present study was aimed to use functional magnetic resonance imaging to reveal the underlying functional integration within the prefrontal cortex during the task which requires that subjects to deliberately mislead an opponent through the sequential execution of deceptive and honest claims. To address this issue, we performed psychophysiological interaction (PPI) analysis, which allows for statistical assessment of changes in functional relationships between active brain areas in changing psychological contexts. As a result the whole brain PPI-analysis established that both manipulative honest and deceptive claiming were associated with an increase in connectivity between the left middle frontal gyrus and right temporo-parietal junction (rTPJ). Taking into account the role played by rTPJ in processes associated with the theory of mind the revealed data can reflect possible influence of socio-cognitive context on the process of selecting manipulative claiming regardless their honest or deceptive nature. Direct comparison between deceptive and honest claims revealed pattern enhancement of coupling between the left middle frontal gyrus and the left inferior frontal gyrus. This finding provided evidence that the execution of deception relies to a greater extent on higher-order hierarchically-organized brain mechanisms of executive control required to select between two competing deceptive or honest task sets.

Functional Interactions between the Caudate Nuclei and Inferior Frontal Gyrus Providing Deliberate Deception

The goal of the present study was to investigate functional interactions between brain structures during deliberate deception. On the basis of the results obtained and literature data, the following hypothesis has been formulated: the functional interaction between the brain areas responsible for executive control of the behavior localized in the prefrontal cortex (inferior frontal gyrus) and elements of the error detection system of the brain underlie deliberate deception. This hypothesis has been tested using psychophysiological interaction (PPI) analysis, which has revealed that deceptive actions (in comparison to truthful ones) are related to an increased functional connectivity between the left caudate nucleus and left inferior frontal gyrus. The experimental data support our hypothesis that the interaction of the brain systems responsible for executive control and error detection underpins the brain maintenance of execution of deceptive actions.

Contemporary Methods for Functional Tomographic Neuroimaging in Studies of Brain Functions in Health and Pathology

Contemporary functional tomographic neuroimaging methods (fMRI and PET) have for many years been applied actively not only in basic studies of brain functions, but also in clinical practice. This article considers the main characteristics of the signals recorded and the principles of constructing images, as well as the requirements for obtaining adequate results. The advantages and fundamental limitations of contemporary tomographic methods of studying brain functions are discussed. The need to use complex approaches consisting of combined studies in investigating the brain is demonstrated, and methods for studying the functional integration of the brain are proposed.

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.