Electroencephalography (EEG) is the recording of electrical activity of the brain. The technique was invented in 1929 by Hans Berger, who discovered that there was a difference in electrical potential between needles infixed to the scalp or between two small metal disks (electrodes) when they were placed on the scalp. At the base of every conscious and unconscious mental function is electrical communication between neurons. It is not possible to record the electrical activity of the single neuron in a non-invasive way, however the EEG allows to measure the fluctuations of electrical potential above the scalp caused by the simultaneous electrical activity of a population of neurons. Such potential fluctuations may be characterized in terms of spectral content (EEG bands or rhythms) or of time domain characteristics (Evoked Potentials and Event-related). The spontaneous brain electrical activity of a particular area in a particular frequency band can be associated with specific cognitive processes and mental states. The analysis of Evoked Potentials consists in mediating the synchronous EEG activity with the presentation of an external stimulus of various kinds. The Event-Related Potentials refer to the synchronous EEG responses with more complicated processes of external stimuli. In addition to clinical applications, thanks to its advantages that also include high temporal resolution, low costs, wide diffusion and non-invasiveness, the EEG technique is widely used in research in many areas of neuroscience.
Electromyography (EMG), electroneurography (ENG) and single fiber electromyography (SFEMG) are neurophysiological methods that are used to study the peripheral nervous system from a functional point of view. It is a reliable method that can provide information on the functionality of peripheral nerves and skeletal muscles. It is also a diagnostic tool that allows to frame the neurological diseases of the peripheral nervous system concerning pathologies of nerve roots, nervous plexuses, peripheral nerves, neuromuscular plaque and muscles. If the neurological examination shows a deficit in the peripheral nervous system, electromyography is an indispensable means to deepen the diagnosis, especially when they are not clear: the site of injury, the extent and type of injury.
Non-invasive brain stimulation (NIBS) aims to inject non-invasively (ie completely harmless to the subject) a series of stimuli with a facilitatory or inhibitory action in an area of the brain below the stimulation point; if this area is a “node” of a network, the stimulus is able to modulate (facilitate/inhibit) the effectiveness of the network, determining changes in behavioral responses and cognitive processes related to it (network). NIBS techniques include transcranial magnetic stimulation (TMS) and transcranial electrical stimulation with direct current (tDCS) and alternating current (tACS).
Allows the study of the physiology of cerebral cortical activity in vivo in a non-invasive way. It is based on the principle of electromagnetic induction of a field whose function is to be able to stimulate the cells of the cortex obtaining a potential evoked in response. Through its application, it is possible to investigate the functioning of synaptic connections and brain plasticity.
Transcranial stimulation with direct currents or tDCS is a non-invasive and painless neurostimulation method that allows to modulate cortical excitability through continuous currents at low intensity. It consists in the application on the scalp of electrodes providing a low intensity direct current able to cross the scalp and influence the neuronal functions.
Like tDCS, the tACS (transcranial alternating current stimulation) is a non-invasive and painless neuro modulation method that allows to apply variable-frequency currents able to interact with the natural frequencies of cerebral oscillation. Thanks to the possibility of acting on a large frequency range, it allows to act on the synchronization (with a single resonance frequency) and on the desynchronization (by applying multiple frequencies) of the cortical oscillations. If applied for a long time it can cause neuroplastic effects.