50 research outputs found
Phantasy, Multiverse and Protopia: Ran Slavin's Israeli Futurism
No full textThe essay discusses Israeli artist Ran Slavin's transmedia production, since the 1990s, as a key example of Israeli Futurism. The essay contextualizes Slavin's films, multimedia installations, photography, soundscapes, CGI imagery, and tech-based output as a way to process the conflictual dynamics at the basis of the foundation of Israel, the mythologies of Judaism and the ongoing metamorphosis of Jewish identity. The author of this essay, Francesco Spampinato, is also the editor of this major retrospective monograph on Slavin's work
Dissecting two distinct interneuronal networks in M1 with transcranial magnetic stimulation
No full textInteractions from both inhibitory and excitatory interneurons are necessary components of cortical processing that contribute to the vast amount of motor actions executed by humans daily. As transcranial magnetic stimulation (TMS) over primary motor cortex is capable of activating corticospinal neurons trans-synaptically, studies over the past 30 years have provided how subtle changes in stimulation parameters (i.e., current direction, pulse width, and paired-pulse) can elucidate evidence for two distinct neuronal networks that can be probed with this technique. This article provides a brief review of some fundamental studies demonstrating how these networks have separable excitatory inputs to corticospinal neurons. Furthermore, the findings of recent investigations will be discussed in detail, illustrating how each network’s sensitivity to different brain states (i.e., rest, movement preparation, and motor learning) is dissociable. Understanding the physiological characteristics of each network can help to explain why interindividual responses to TMS exist, while also providing insights into the role of these networks in various human motor behaviors
Alzheimer disease and neuroplasticity
No full textAlzheimer's disease (AD) is considered the most harmful form of dementia in the elderly population. At present, there are no effective treatments and this is likely due to the incomplete understanding of the pathophysiology. Recent data indicate that synaptic dysfunction could be a central element of AD pathophysiology. It was found that a synaptic breakdown is an early event that heralds neuronal degeneration. Transcranial magnetic stimulation (TMS) has been recently introduced as a novel approach to identify the early signatures of synaptic dysfunction characterizing AD pathophysiology. In this chapter, we review the new neurophysiologic signatures of AD that have been emphasized by TMS studies. We show how TMS measurement of neuroplasticity identified long-term potentiation (LTP)-like cortical plasticity as a key element of AD synaptic dysfunction. These measurements are useful to increase the accuracy of differential diagnosis, predict disease progression, and anticipate response to therapy. Moreover, enhancing neuroplasticity holds as a promising therapeutic approach to improve cognition in AD. In recent years, studies showed treatments with multiple sessions of rTMS can influence cognition in people with neurodegenerative diseases. In the second part of this chapter, we also consider novel therapeutic approaches based on the clinical use of rTMS
Multiple Motor Learning Processes in Humans: Defining Their Neurophysiological Bases
No full textLearning new motor behaviors or adjusting previously learned actions to account for dynamic changes in our environment requires the operation of multiple distinct motor learning processes, which rely on different neuronal substrates. For instance, humans are capable of acquiring new motor patterns via the formation of internal model representations of the movement dynamics and through positive reinforcement. In this review, we will discuss how changes in human physiological markers, assessed with noninvasive brain stimulation techniques from distinct brain regions, can be utilized to provide insights toward the distinct learning processes underlying motor learning. We will summarize the findings from several behavioral and neurophysiological studies that have made efforts to understand how distinct processes contribute to and interact when learning new motor behaviors. In particular, we will extensively review two types of behavioral processes described in human sensorimotor learning: (1) a recalibration process of a previously learned movement and (2) acquiring an entirely new motor control policy, such as learning to play an instrument. The selected studies will demonstrate in-detail how distinct physiological mechanisms contributions change depending on the time course of learning and the type of behaviors being learned
Motor potentials evoked by transcranial magnetic stimulation: interpreting a simple measure of a complex system
No full textTranscranial magnetic stimulation (TMS) is a non‐invasive technique that is increasingly used to study the human brain. One of the principal outcome measures is the motor‐evoked potential (MEP) elicited in a muscle following TMS over the primary motor cortex (M1), where it is used to estimate changes in corticospinal excitability. However, multiple elements play a role in MEP generation, so even apparently simple measures such as peak‐to‐peak amplitude have a complex interpretation. Here, we summarize what is currently known regarding the neural pathways and circuits that contribute to the MEP and discuss the factors that should be considered when interpreting MEP amplitude measured at rest in the context of motor processing and patients with neurological conditions. In the last part of this work, we also discuss how emerging technological approaches can be combined with TMS to improve our understanding of neural substrates that can influence MEPs. Overall, this review aims to highlight the capabilities and limitations of TMS that are important to recognize when attempting to disentangle sources that contribute to the physiological state‐related changes in corticomotor excitability
Frequency-dependent modulation of cerebellar excitability during the application of non-invasive alternating current stimulation
No full textBACKGROUND: it is well-known that the cerebellum is critical for the integrity of motor and cognitive actions. Applying non-invasive brain stimulation techniques over this region results in neurophysiological and behavioural changes, which have been associated with the modulation of cerebellar-cerebral cortex connectivity. Here, we investigated whether online application of cerebellar transcranial alternating current stimulation (tACS) results in changes to this pathway. METHODS: thirteen healthy individuals participated in two sessions of cerebellar tACS delivered at different frequencies (5Hz and 50Hz). We used transcranial magnetic stimulation to measure cerebellar-motor cortex (M1) inhibition (CBI), short-intracortical inhibition (SICI) and short-afferent inhibition (SAI) before, during and after the application of tACS. RESULTS: we found that CBI was specifically strengthened during the application of 5Hz cerebellar tACS. No changes were detected immediately following the application of 5Hz stimulation, nor at any time point with 50Hz stimulation. We also found no changes to M1 intracortical circuits (i.e. SICI) or sensorimotor interaction (i.e. SAI), indicating that the effects of 5Hz tACS over the cerebellum are site-specific. CONCLUSIONS: cerebellar tACS can modulate cerebellar excitability in a time- and frequency-dependent manner. Additionally, cerebellar tACS does not appear to induce any long-lasting effects (i.e. plasticity), suggesting that stimulation enhances oscillations within the cerebellum only throughout the stimulation period. As such, cerebellar tACS may have significant implications for diseases manifesting with abnormal cerebellar oscillatory activity and also for future behavioural studies
P153 Cerebellar-M1 connectivity (CBI): One or two different networks?
No full textIntroduction Recently it has been argued that two distinct interneuron networks in the primary motor cortex (M1) contribute distinctly to two varieties of physiological plasticity and motor behaviors (Hamada et al., 2014). Although one of the interneuron groups is thought to be dependent on cerebellar (CB) activity, direct physiological distinction regarding CB-M1 interactions (CBI) to these subpopulations remains poorly understood. Objectives This study assessed whether M1 coil orientation, thought to test different neuronal populations, affects CBI in the context of two motor behaviors that weight differently cerebellar vs. M1 contributions. Methods In experiment 1 (n = 10), we tested the effect of coil orientation (posterior–anterior, PA; anterior–posterior, AP) and inter-stimulus intervals (ISI: 3, 5 and 7 ms) on CBI; assessed with a conditioned TMS pulse over the cerebellum prior to TMS over the contralateral M1. In experiment 2 (n = 10), we tested how learning two distinct motor learning tasks (weighting sensorimotor calibration vs. a sequence task) affected AP- vs. PA-CBI measured at their preferential ISI. Results ANOVA-RM revealed a significant CBI effect for ISI (F(2,36) = 17.807; p < 0.01) and COIL ORIENTATION*ISI interaction (F(2,36) = 8.067; p = 0.01). Specifically, PA-CBI was prominent at 5 ms ISI (p = 0.02) and AP-CBI at 7 ms ISI (p = 0.01). To determine how learning affects AP- vs. PA-CBI at their preferential ISI, we compared CBI before, during and after training. ANOVA-RM revealed a significant effect of CBI for MOTOR TASK*TIME*ORIENTATION interaction (F(4,42) = 2.800; p = 0.04). When learning a sensorimotor calibration, PA-CBI changed only early during learning (p = 0.02), whereas AP-CBI changed only late (p = 0.01). Additionally, during sequence learning, PA-CBI also changed only early (p = 0.01), whereas AP-CBI was not modulated. Conclusion These findings indicate that CB-M1 interactions are different for the two M1 neural networks. This could be the result of either two independent CB-M1 pathways or distinct processing of cerebellar inputs within M1
SICI during changing brain states: Differences in methodology can lead to different conclusions
No full textBackground
Short-latency intracortical inhibition (SICI) is extensively used to probe GABAergic inhibitory mechanisms in M1. Task-related changes in SICI are presumed to reflect changes in the central excitability of GABAergic pathways. Usually, the level of SICI is evaluated using a single intensity of conditioning stimulus so that inhibition can be compared in different brain states.
Objective
Here, we show that this approach may sometimes be inadequate since distinct conclusions can be drawn if a different CS intensity is used.
Methods
We measured SICI using a range of CS intensities at rest and during a warned simple reaction time task.
Conclusions
Our results show that SICI changes that occurred during the task could be either larger or smaller than at rest depending on the intensity of the CS. These findings indicate that careful interpretation of results are needed when a single intensity of CS is used to measure task-related physiological changes
Cerebellar–Motor Cortex Connectivity: One or Two Different Networks?
No full textAnterior–posterior (AP) and posterior–anterior (PA) pulses of transcranial magnetic stimulation (TMS) over the primary motor cortex (M1) appear to activate distinct interneuron networks that contribute differently to two varieties of physiological plasticity and motor behaviors (Hamada et al., 2014). The AP network is thought to be more sensitive to online manipulation of cerebellar (CB) activity using transcranial direct current stimulation. Here we probed CB–M1 interactions using cerebellar brain inhibition (CBI) in young healthy female and male individuals. TMS over the cerebellum produced maximal CBI of PA-evoked EMG responses at an interstimulus interval of 5 ms (PA-CBI), whereas the maximum effect on AP responses was at 7 ms (AP-CBI), suggesting that CB–M1 pathways with different conduction times interact with AP and PA networks. In addition, paired associative stimulation using ulnar nerve stimulation and PA TMS pulses over M1, a protocol used in human studies to induce cortical plasticity, reduced PA-CBI but not AP-CBI, indicating that cortical networks process cerebellar inputs in distinct ways. Finally, PA-CBI and AP-CBI were differentially modulated after performing two different types of motor learning tasks that are known to process cerebellar input in different ways. The data presented here are compatible with the idea that applying different TMS currents to the cerebral cortex may reveal cerebellar inputs to both the premotor cortex and M1. Overall, these results suggest that there are two independent CB–M1 networks that contribute uniquely to different motor behaviors
Investigating the effects of paired somatosensory - cerebellar stimulation on cortical and cerebellar excitability: a TMS study
No full textIt is well known that paired associative stimulation (PAS) is capable of inducing long term potentiation-like synaptic plasticity when repeated pairings of an electrical stimulus to the median nerve with a transcranial magnetic stimulation (TMS) applied over the motor cortex (M1) is administered between 21-25 ms (Stefan et al., 2000). Interestingly, when PAS is administered at 25 ms, cerebellar activity can abolish PAS after-effects (Hamada et al., 2012). While this suggests that cerebellar activity may influence the arrival of sensory inputs to the sensorimotor cortex, this has not been directly tested using physiological markers of somatosensory and cerebellar inputs to M1 or somatosensory cortex (S1).
Since the cerebellum is capable of priming M1 plasticity through the processing of sensory information, we investigated whether the continuous pairing of sensory afferent information with cerebellar stimulation influences the plasticity of both cerebellar and cerebral regions. We tested whether sensory inputs could be paired with cerebellar stimulation to develop a novel PAS protocol. To this aim, electrical stimulation to the median nerve was delivered 10 or 15 ms before applying TMS over the cerebellum (200 paired stimuli). We measured motor evoked potentials (MEPs) and somatosensory evoked potentials (SEPs) as physiological markers of cortical excitability, cerebellum-brain inhibition (CBI) as a marker of cerebellar excitability, and short afferent inhibition (SAI) as a marker of somatosensory inhibition, before and following PAS. Preliminary results showed that sensory-cerebellar PAS significantly modifies M1 excitability, reducing MEP amplitude and increasing SEP amplitude. This effect occurs only when the PAS interval was 10ms, but not at 15ms. Moreover, CBI and SAI were unchanged following PAS.
The repetitive pairing of both somatosensory and cerebellar stimulation can induce plasticity effects on cerebral areas. The results of sensory-cerebellar PAS could provide a useful intervention with clinical implications for patients with sensory-motor deficits such as dystonia
