Evgeny Blagovechtchenski

Skilled digit movements in feline and primate--recovery after selective spinal cord lesions.

Recovery of voluntary movements after partial spinal cord injury depends, in part, on a take‐over of function via unlesioned pathways. Using precise forelimb movements in the cat as model, spinal pathways contributing to motor restitution have been investigated in more detail. The food‐taking movement by which the cat graSPS a morsel of food with the digits and brings it to the mouth is governed by interneurones in the forelimb segments (C6‐Th1) and is normally controlled via the cortico‐ and rubrospinal tracts. Food‐taking disappears after transection of these pathways in the dorsal part of the lateral funiculus (DLF) in C5/C6, but then recovers during a period of 2–3 weeks. Experiments with double lesions showed that the recovery depends on a take‐over via ipsilateral ventral systems; a ventrally descending pathway, most probably cortico‐reticulospinal, and a pathway via propriospinal neurones in the C3–C4 segments. It is postulated that the recovery involves a plastic reorganization of these systems. Dexterous finger movements in the macaque monkey are generally considered to depend on the monosynaptic cortico‐motoneuronal (CM) connexion, which is lacking in the cat. Such movements are abolished after pyramidotomy at the level of the trapezoid body. However, experiments with transection of the corticospinal tract in the DLF and partly ventral part of the lateral funiculus in C5, showed a fast (1–28 days) recovery of precision grip and, to some extent, independent finger movements. Deficits in preshaping during the final approach to the morsel as well as lack of force were observed. A C5 DLF lesion spares corticofugal pathways to the brainstem and upper cervical segments. It is suggested that indirect corticomotoneuronal pathways may provide for recovery of dexterous finger movements and that the role of CM pathways for such movements should be broadened to include not only the monosynaptic connexion.

Pre-stimulus Alpha Oscillations and Inter-subject Variability of Motor Evoked Potentials in Single- and Paired-Pulse TMS Paradigms

Inter- and intra-subject variability of the motor evoked potentials (MEPs) to TMS is a well-known phenomenon. Although a possible link between this variability and ongoing brain oscillations was demonstrated, the results of the studies are not consistent with each other. Exploring this topic further is important since the modulation of MEPs provides unique possibility to relate oscillatory cortical phenomena to the state of the motor cortex probed with TMS. Given that alpha oscillations were shown to reflect cortical excitability, we hypothesized that their power and variability might explain the modulation of subject-specific MEPs to single- and paired-pulse TMS (spTMS, ppTMS, respectively). Neuronal activity was recorded with multichannel electroencephalogram. We used spTMS and two ppTMS conditions: intracortical facilitation (ICF) and short-interval intracortical inhibition (SICI). Spearman correlations were calculated within and across subjects between MEPs and the pre-stimulus power of alpha oscillations in low (8–10 Hz) and high (10–12 Hz) frequency bands. Coefficient of quartile variation was used to measure variability. Across-subject analysis revealed no difference in the pre-stimulus alpha power among the TMS conditions. However, the variability of high-alpha power in spTMS condition was larger than in the SICI condition. In ICF condition pre-stimulus high-alpha power variability correlated positively with MEP amplitude variability. No correlation has been observed between the pre-stimulus alpha power and MEP responses in any of the conditions. Our results show that the variability of the alpha oscillations can be more predictive of TMS effects than the commonly used power of oscillations and we provide further support for the dissociation of high and low-alpha bands in predicting responses produced by the stimulation of the motor cortex.

Recovery of food-taking in cats after lesions of the corticospinal (complete) and rubrospinal (complete and incomplete) tracts

The food-taking movement by which a cat grasps a morsel of food and brings it to the mouth is governed by interneurones in the forelimb segments (C6-Th1) and is normally controlled by the cortico- and rubrospinal tracts. It disappears reversibly when these tracts are transected in C5. The reappearance after some time is at least in part due to a reticulospinal take-over of the command. We have compared the recovery after total transection of both tracts with that after lesions giving subtotal transection of the rubrospinal tract but total transection of the corticospinal tract. With 4-6% of the rubrospinal fibres left, the recovery of food-taking was clearly faster than after total transection.

Control of digits via C3-C4 propriospinal neurones in cats; recovery after lesions.

C3-C4 propriospinal neurones (C3-C4 PNs) transmit the command for forelimb target-reaching in cats, while the command for food-taking is mediated by interneurones in the forelimb segments. The ability of the C3-C4 PNs to control digits has now been reinvestigated with combined lesions in dorsal C5 (transecting the cortico- and rubrospinal tracts) and ventral C2 (transecting reticulospinal tracts) leaving the C3-C4 PNs in sole control of the forelimb. Components of food-taking like flexion in the proximal interphalangeal joints were found in half of the cats. Supination and terminal flexion of the metacarpophalangeal joints by which normal cats bring the morsel of food to the mouth were lacking in all cats.

Long-Range Temporal Correlations in the amplitude of alpha oscillations predict and reflect strength of intracortical facilitation: Combined TMS and EEG study

While variability of the motor responses to transcranial magnetic stimulation (TMS) is widely acknowledged, little is known about its central origin. One plausible explanation for such variability may relate to different neuronal states defining the reactivity of the cortex to TMS. In this study intrinsic spatio-temporal neuronal dynamics were estimated with Long-Range Temporal Correlations (LRTC) in order to predict the inter-individual differences in the strength of intra-cortical facilitation (ICF) and short-interval intracortical inhibition (SICI) produced by paired-pulse TMS (ppTMS) of the left primary motor cortex. LRTC in the alpha frequency range were assessed from multichannel electroencephalography (EEG) obtained at rest before and after the application of and single-pulse TMS (spTMS) and ppTMS protocols. For the EEG session, preceding TMS application, we showed a positive correlation across subjects between the strength of ICF and LRTC in the fronto-central and parietal areas. This in turn attests to the existence of subject-specific neuronal phenotypes defining the reactivity of the brain to ppTMS. In addition, we also showed that ICF was associated with the changes in neuronal dynamics in the EEG session after the application of the stimulation. This result provides a complementary evidence for the recent findings demonstrating that the cortical stimulation with sparse non-regular stimuli might have considerable long-lasting effects on the cortical activity.

Neural mechanisms of cognitive dissonance (revised): An EEG study.

Cognitive dissonance theory suggests that our preferences are modulated by the mere act of choosing. A choice between two similarly valued alternatives creates psychological tension (cognitive dissonance) that is reduced by a postdecisional reevaluation of the alternatives. We measured EEG of human subjects during rest and free-choice paradigm. Our study demonstrates that choices associated with stronger cognitive dissonance trigger a larger negative frontocentral evoked response similar to error-related negativity, which has in turn been implicated in general performance monitoring. Furthermore, the amplitude of the evoked response is correlated with the reevaluation of the alternatives. We also found a link between individual neural dynamics (long-range temporal correlations) of the frontocentral cortices during rest and follow-up neural and behavioral effects of cognitive dissonance. Individuals with stronger resting-state long-range temporal correlations demonstrated a greater postdecisional reevaluation of the alternatives and larger evoked brain responses associated with stronger cognitive dissonance. Thus, our results suggest that cognitive dissonance is reflected in both resting-state and choice-related activity of the prefrontal cortex as part of the general performance-monitoring circuitry. SIGNIFICANCE STATEMENT Contrary to traditional decision theory, behavioral studies repeatedly demonstrate that our preferences are modulated by the mere act of choosing. Difficult choices generate psychological (cognitive) dissonance, which is reduced by the postdecisional devaluation of unchosen options. We found that decisions associated with a higher level of cognitive dissonance elicited a stronger negative frontocentral deflection that peaked ∼60 ms after the response. This activity shares similar spatial and temporal features as error-related negativity, the electrophysiological correlate of performance monitoring. Furthermore, the frontocentral resting-state activity predicted the individual magnitude of preference change and the strength of cognitive dissonance-related neural activity.

Real time adenosine fluctuations detected with fast-scan cyclic voltammetry in the rat striatum and motor cortex.

BACKGROUND Adenosine serves many functions within the CNS, including inhibitory and excitatory control of neurotransmission. The understanding of adenosine dynamics in the brain is of fundamental importance. The goal of the present study was to explore subsecond adenosine fluctuations in the rat brain in vivo. METHOD Long Evans rats were anesthetized and a carbon fiber electrode was positioned in the motor cortex or dorsal striatum. Real time electrochemical recordings were made at the carbon fiber electrodes every 100ms by applying a triangular waveform (-0.4 to +1.5V, 400V/s). Adenosine spikes were identified by the background-subtracted cyclic voltammogram. RESULTS The frequency of detected adenosine spikes was relatively stable in both tested regions, and the time intervals between spikes were regular and lasted from 1 to 5s within an animal. Spike frequency ranged from 0.5 to 1.5Hz in both the motor cortex and the dorsal striatum. Average spike amplitudes were 85±11 and 66±7nM for the motor cortex and the dorsal striatum, respectively. COMPARISON WITH EXISTING METHODS The current study established that adenosine signaling can operate on a fast time scale (within seconds) to modulate brain functions. CONCLUSIONS This finding suggests that spontaneous adenosine release may play a fast, dynamic role in regulating an organisms response to external events. Therefore, adenosine transmission in the brain may have characteristics similar to those of classical neurotransmitters, such as dopamine and norepinephrine.

Modern Brain Mapping - What Do We Map Nowadays?

The problem of function localization in the brain is one of the most fundamental in neuroscience. There are two opposite paradigms relating to the problem: “modularism,” also known as “localism,” versus “holism,” which have been discussed for a long time (1, 2). The debate in favor of one or another view can still be traced at all methodological levels – from the cell to the system. In this opinion paper we want to raise a question – what is meant nowadays by brain mapping? In addition, we want to highlight the necessity of being aware of occasionally occurring discontinuity in the research at different methodological scales. This problem is evident for experts in the field, but not always sufficiently so for early career researches. We will try to describe the difficulties of modern brain mapping primarily by looking at one of the currently best-studied functions – motor function.

Erratum to “Control of digits via C3–C4 propriospinal neurones in cats; recovery after lesions”

Fig. 1. Histological (A–D) and electrophysiological (E, F) control of lesions in dorsal C5 and ventral C2. The electrophysiological controls, obtained with stimulation of the contralateral (co) red nucleus (NR) and co pyramid (Pyr), are from cat 2 illustrated in Fig. 3. Upper traces show the maximal volleys (negativity upwards) on the unlesioned control side and lower traces the recordings from the lesioned side (negativity downwards). Note normal discharges in the corticoand rubrospinal tracts on the control side but absence of them on the lesioned side, showing complete transection of both tracts. The histological controls in the four remaining cats showed that the extents of the lesions were in between those in cat 2 and cat 3.

Rapid communicationErratum to “Control of digits via C3–C4 propriospinal neurones in cats; recovery after lesions”: [Neuroscience Research 38 (2000) 103–108]

Fig. 1. Histological (A–D) and electrophysiological (E, F) control of lesions in dorsal C5 and ventral C2. The electrophysiological controls, obtained with stimulation of the contralateral (co) red nucleus (NR) and co pyramid (Pyr), are from cat 2 illustrated in Fig. 3. Upper traces show the maximal volleys (negativity upwards) on the unlesioned control side and lower traces the recordings from the lesioned side (negativity downwards). Note normal discharges in the corticoand rubrospinal tracts on the control side but absence of them on the lesioned side, showing complete transection of both tracts. The histological controls in the four remaining cats showed that the extents of the lesions were in between those in cat 2 and cat 3.