Can the brain be stimulated through vision? That was the question that motivated our study recently published in Journal of Imagingwhere it is demonstrated that intermittent visual stimulation can modulate brain activity, a functional plasticity marker. This can be understood as the ability of the brain to change its structure and adapt during life. Thanks to this, our neurons can eliminate those that we do not use or strengthen the connections that allow us learning, memory or recover from injuries such as speech loss after suffering a stroke.
The good news is that plasticity is not exclusive to children’s age, but that the brain in adulthood continues to reorganize its connections. His study, however, usually requires complex and expensive techniques, in certain cases, invasive.
The method: confront the visual system
The intermittent luminous stimulation consists in exposing the observer to a light that blinks at a certain frequency. Meanwhile, brain activity is measured by electroencephalography (EEG) and is compared to the activity under normal conditions.
If during stimulation, an answer known as visual evoked potentials is observed, we understand that there has been an answer in the cerebral cortex through the visual system due to the flash stimulus: a greater response implies greater excitability and, therefore, functional plasticity.
Critical Fusion Frequency
The key is at the frequency of the flickering of light. Our visual system presents two main roads, which transmit the information from the retina to the brain, known as “parvocellular” and “magnocellular” roads. In summary, the first is sensitive to high spatial resolution (fine details) and slow temporary changes. The second responds to low spatial resolution and rapid temporal changes. Both work in a complementary way.
However, sometimes, the movement is so fast that our visual system cannot process the speed (such as a very fast flicker), or the image quality degrades so much that we cannot perceive small details (as with the cataracts, or the driving on a day of fog). In these scenarios, our visual system reaches the resolution limit leading to a phenomenon known as spatial and temporal “summation”. That is, our brain “adds” the signals it receives to generate an answer.
In the case of spatial vision, it translates into a blurred stain. In the temporal case, a light blinking at a very high frequency is perceived as a static light without any flashing. This frequency in the visual system is generally above 30 Hz and is known as critical fusion frequency.
In these space-time limits of the vision, the parvo and mageno-cellular roads play a compensatory role: if the spatial resolution decreases, the temporal increases, and vice versa. .
In our brain, there are cortical sensitivity windows where stimulation with certain frequencies induce the neuronal response, while others can inhibit it or even be harmless.
Stimulate brain without invasive therapies
Neurons are not activated randomly: they do so following oscillatory patterns – repetitive – of electrical activity. These oscillations are of very low amplitude, of the order of microvolts in humans. The analysis of wave patterns is a great research tool in neurophysiology to evaluate how the brain works. In most cerebral cortex pathologies, decreased waves are observed.
These waves of brain electrical activity are detected by EEG and, according to their oscillation frequency, are classified as Alfa, Theta, Delta, Beta and Gamma waves. In our study, we verify that all can be modulated by visual stimuli. We present to the participants visual stimuli based on a flashing LED controlled by a low -cost mini -priest (Arduino) and we find that, by stimulating the critical fusion vision with a green light, there was a significant reduction of high frequency and gamma high frequency waves.
However, by decreasing the amount of light emitted by translucent light diffusers, the compensatory nature of the magno and cell turkey is compromised. This confrontation helped us to detect an antagonistic response mechanism in brain activity: a significant increase in the neuronal activity of beta and gamma waves was found.
Cortical activity maps for lighting at critical frequency with green light (right) and when the parvocellular system is penalized by optical filters. FJ Ávila et al.
Mental and neurological disorders
The neuronal synchronization of beta and gamma frequency is related to cognitive function and perception, while the loss of synchronization in the gamma band is associated with diseases such as Alzheimer’s, autism and schizophrenia.
In addition, excessive activation of beta waves can generate anxiety and stress, while its inhibition can lead to severe depression and cognitive deterioration.
ELECTRO-ECLEPHALOGRAM OF GAMMA Wave in a healthy subject in resting conditions (red curve) and while the visual stimulator (blue curve) is applied. FJ Ávila et al.
Therefore, high frequency brain waves are important mental health bio-markers.
ELECTRO-ECLEPHALOGRAM OF GAMMA Wave in a healthy subject in resting conditions (red curve) and while the visual stimulator (blue curve) is applied. FJ Ávila et al.
A therapy based on light pulses?
Our experiment was simple, but its implications can be deep: a brief visual stimulation can change, at least temporarily, brain activity. That capacity for change is what we have called visual neuroplasticity.
If we managed to refine that relationship, we could restore lost plasticity, without the need for invasive interventions, to reactivate a sleeping neuronal network.
This article was originally published in The Conversation.
Sign up in the Newsletter Gulp of the counterAdm our community to tell you the most interesting of the world of culture, science and technology.