Brain oscillations, rhythmic stimulation and non-Invasive sensory entrainment

The functional architecture of perception is supported by distinct neurophysiological rhythms organized across different spatial scales \cite{buzsaki2004large}. This essential function -potentially supporting all cognitive activity- has its basis that start from a single neuron \cite{Hutcheon_2000} passing through different neural circuits \cite{Whittington_1997} to thalamo-cortical and cortico-cortical networks \cite{L_rincz_2009}. Thus, different brain rhythms occur at distinct frequency bands as a function of micro- and macro-network architecture \cite{buzsaki2004large}. Different aspects of cognitive activity can thus be described in terms of neuronal oscillators, hierarchically organized interacting at different frequencies \cite{buzsaki2004large}. A biological mechanism named synchronization of neuronal elements enables the dynamic perceptual framing of sensory information (Varela 1981); a neurophysiological process derived from oscillatory coordination \cite{Jensen_2010,Salinas_2001,fries2005mechanism}. Within this neural mechanism, temporal segmentation serves to reduce the problem of information overload because sensory stimuli can be processed serially. In this context synchronous voltage variations that occurring within 8-13 Hz in adults and within 6-9 Hz in children, known as alpha oscillations are thought to be a crucial element or these processes \cite{Palva2007}. Furthermore, these lower frequency rhythms (theta 4-8 Hz, alpha 8-13 Hz) have been related to long-distance brain communication dynamics, while higher frequency bands like gamma (>30 Hz) have been associated with local neuronal interaction \cite{von_Stein_2000}. It has been proposed that low- and high-frequency oscillatory systems belong to a larger multi-band coordination system, enacting an informational multiplexing mechanism \cite{Akam_2014} through cross-frequency interactions \cite{Palva2007,Jensen_2007,Canolty_2010}. Activity in different frequencies across brain structures may also provide important clues to these functions, for instance posterior alpha-band oscillations (8–12 Hz) are related to the sensory input regulation \cite{L_rincz_2009}, and attentional selection \cite{Thut_2009,Worden_2000,Sauseng_2005,Kelly_2006}. Hence, when perception unfolds during driving activities, also relies on processes that enable effective selection and integration of relevant information from the vast amount of sensory inputs on the road, that is constantly bombarding the driver's brain. Sensory function improvements could be therefore made by a natural property of oscillations. This is, oscillatory activity is self-sustained and dynamic (e.g. \cite{pikovsky2003synchronization,Glass_2001}), implying that brain rhythms could be modulated by an external sources. For instance, if the modulation is carried out periodically by an external stimulus, the ongoing waves may then become synchronized to the external patterns. In other words, brain rhythms will synchronously cycle with the same period as the external sensory input, becoming “entrained ” and coordinated to the rhythm of external incoming events \cite{Lakatos_2008}. Within this context, synchronization and entrainment are synonymous \cite{pikovsky2003synchronization}. Thus, in this perspective we will use the term entrainment to refers synchronization to a natural brain rhythmic with rhythm of external (sensory) incoming events.
RE-ESCRIBIR, NO SE ENTIENDE --> [Therefore, generating non-invasive stimulation of a coordinated nature pulsed sensory stimulation appear as key tool for simultaneously entrain many primary sensory structures and input pathways including sub-cortically and cortical structures. In this context pulsed form of rhythmic stimulation is steady-state sensory stimuli presentation.] For instance, transient visual events that are repeated at fixed frequency \cite{Herrmann_2001}, in order to entrain the natural brain frequencies to the rhythm of the presentation. With this non-invasive approach to sensory stimulation, stimuli can be presented in a wide range of repetition frequencies, covering the physiological range of brain oscillations from slow-waves to high-frequencies bands \cite{Herrmann_2001,Thut_2009}, allowing non-invasive brain stimulation at appropriate frequencies and temporal scales. Likewise, inducing sensory entrainment on drivers' brains appear as a perfect candidate to generate non-invasive safety tools for prevention of automobile accident. In addition, note the possibility of generating a tool in road infrastructure to modify and improve the perceptual and behavioral performance of drivers appears as a neuroergonomic challenge in urban design, as well also opening a new path in the way the concept of road safety is constructed, designed from and for the human brain.