Effects of static magnetic field stimulation over the motor cortex on the excitability of the short afferent inhibitory circuits

[Abstract] Static magnetic fields have shown to be able to modulate of motor cortex excitability, and their effects remain for a period that outlasts the time of the application of the magnetic field. In the present study we tried to find out if the cortex excitability change induced by static magnetic fields could produce effects on short latency afferent inhibition circuits. Short latency afferent inhibition is a cortical inhibition which has been proved by electromyographic recordings in motor evoked potentials generated by transcraneal magnetic stimulation, if combined with percutaneous electric stimulation on a mixed nerve. This inhibitory effect occurs when the electric stimulation is delivered around 20ms before the magnetic pulse. We evaluated short latency afferent inhibition before and after the application of a magnetic static field during 20’ (in one session); or a sham (in another session). Data from 8 subjects were analyzed. The data indicated no modulation of short latency afferent inhibition circuits by transcraneal static magnetic stimulation.[Resumen] Los campos magnéticos estáticos han mostrado ser capaces de modificar la excitabilidad cortical, y que sus efectos perduran más allá del tiempo de estimulación. En el presente estudio hemos tratado de averiguar si esta modificación de la excitabilidad cortical produciría efectos sobre los circuitos de inhibición aferente de latencia corta. La inhibición aferente de latencia corta es una inhibición cortical que ha sido comprobada mediante registros electromiográficos de potenciales evocados motores generados por estimulación magnética transcraneal combinada con estimulación eléctrica percutánea sobre un nervio mixto. Este efecto inhibitorio se produce cuando la estimulación eléctrica precede a la magnética alrededor de unos 20ms. El protocolo consistió en evaluación de la inhibición aferente de corta latencia antes y después de la aplicación de un campo magnético estático durante 20’ (en una sesión); o de un placebo (en otra sesión). Fueron analizados los datos correspondientes a 8 sujetos. Los datos no indicaron afectación de los circuitos de inhibición aferente de latencia corta por la estimulación magnética estática transcraneal.Traballo fin de mestrado (UDC.CIE). Neurociencia. Curso 2015/201

The effects of stimulating the cerebellum on social sequences: A tDCS-fMRI pilot study

Research on the involvement of the cerebellum in social behavior and its relationship with social mentalizing has just begun. Social mentalizing is the ability to attribute mental states such as desires, intentions, and beliefs to others. This ability involves the use of social action sequences which are believed to be stored in the cerebellum. In order to better understand the neurobiology of social mentalizing, we applied cerebellar transcranial direct cur-rent stimulation (tDCS) on 23 healthy participants in the MRI scanner, immediately followed by measuring their brain activity during a task that required to generate the correct sequence of social actions involving false (i.e., outdated) and true beliefs, social routines and non-social (control) events. The results revealed that stimulation decreased task performance along with decreased brain activation in mentalizing areas, including the temporo-parietal junction and the precuneus. This decrease was strongest for true belief sequences compared to the other sequences. These findings support the functional impact of the cerebellum on the mentalizing network and belief mentalizing, contributing to the understanding of the role of the cerebellum in social sequences.Research on the involvement of the cerebellum in social behavior and its relationship with social mentalizing has just begun. Social mentalizing is the ability to attribute mental states such as desires, intentions, and beliefs to others. This ability involves the use of social action sequences which are believed to be stored in the cerebellum. In order to better understand the neurobiology of social mentalizing, we applied cerebellar transcranial direct cur-rent stimulation (tDCS) on 23 healthy participants in the MRI scanner, immediately followed by measuring their brain activity during a task that required to generate the correct sequence of social actions involving false (i.e., outdated) and true beliefs, social routines and non-social (control) events. The results revealed that stimulation decreased task performance along with decreased brain activation in mentalizing areas, including the temporo-parietal junction and the precuneus. This decrease was strongest for true belief sequences compared to the other sequences. These findings support the functional impact of the cerebellum on the mentalizing network and belief mentalizing, contributing to the understanding of the role of the cerebellum in social sequences.A

A Functional Atlas of the Cerebellum Based on NeuroSynth Task Coordinates

AbstractAlthough the human cerebellum has a surface that is about 80% of that of the cerebral cortex and has about four times as many neurons, its functional organization is still very much uncharted. Despite recent attempts to provide resting-state and task-based parcellations of the cerebellum, these two approaches lead to large discrepancies. This article describes a comprehensive task-based functional parcellation of the human cerebellum based on a large-scale functional database, NeuroSynth, involving an unprecedented diversity of tasks, which were reliably associated with ontological key terms referring to psychological functions. Involving over 44,500 participants from this database, we present a parcellation that exhibits replicability with earlier resting-state parcellations across cerebellar and neocortical structures. The functional parcellation of the cerebellum confirms the major networks revealed in prior work, including sensorimotor, directed (dorsal) attention, divided (ventral) attention, executive control, mentalizing (default mode) networks, tiny patches of a limbic network, and also a unilateral language network (but not the visual network), and the association of these networks with underlying ontological key terms confirms their major functionality. The networks are revealed at locations that are roughly similar to prior resting-state cerebellar parcellations, although they are less symmetric and more fragmented across the two hemispheres. This functional parcellation of the human cerebellum and associated key terms can provide a useful guide in designing studies to test specific functional hypotheses and provide a reference for interpreting the results.</jats:p

Stimulation of the dorsolateral prefrontal cortex modulates brain cue reactivity to reward (un)availability

Brain imaging studies have shown that stimulation of the left dorsolateral prefrontal cortex (dlPFC), which plays a pivotal role in high-order cognitive control processes, modulates brain reactivity to reward-related cues. Nevertheless, the impact of contextual factors such as reward availability (the reward that is depicted in the cue exposure task) on such modulation effect remains unclear. Here we tested whether a single session of high-frequency repetitive transcranial magnetic stimulation (HF-rTMS) over the left dlPFC differently impacts brain reactivity to cues signalling either availability or unavailability of a sports betting opportunity. Employing a within-subject design (verum versus sham HF-rTMS) among thirty-two frequent sports bettors, we first observed that, as compared to the sham condition, verum HF-rTMS modulated brain reactivity to game cues prior to being made (un)available for betting, through simultaneous increases (posterior insula and caudate nucleus) and decreases (occipital pole) in brain activation. Second, verum HF-rTMS led to increased ventral striatal activity towards cues available for betting but did not modulate brain response to cues unavailable for betting. Third, exploratory functional connectivity analyses revealed increased negative coupling in the verum condition between the left dlPFC and the right and left superior frontal gyrus toward available and non-available betting cues, respectively. Taken together, these findings demonstrate that transient stimulation of the left dlPFC led to a general modulation in brain activity and functional connectivity in responses to cues, and that this effect is only partly dependent on cues signalling for reward (un)availability