Visual stimuli induce gamma waves in our brain

Our brain is a ballroom echoing with humming footsteps of exquisite dancers aka 'brain waves'. Synchronised electrical pulses from neurons communicating with each other produce these brain waves that ricochet throughout the brain. They skilfully route information in a way that allows the brain to choose which signals should be considered vital. Now, a new study by researchers at the Indian Institute of Science, Bengaluru, has revealed how visual stimuli that include TV screens and video games can impact a type of brain waves called gamma waves in primates. The study has been published in The Journal of Neuroscience.

There are five types of brain waves, and each has a role to play in our brain's function. Alpha brainwaves, for example, are responsible for overall mental coordination and learning, while beta brain waves are generated when we are alert, attentive, solving a problem or making decisions. Theta and delta brain waves are low in frequency and occur most often in sleep or deep meditation. Gamma brainwaves have the highest frequency of all and relate to simultaneous processing of information from different brain areas. Scientists think that gamma waves aid in visual perception, feelings and repeating words.

The researchers of this study tested two bonnet macaque monkeys (Macaca radiata) when they were awake and 15 humans to measure their brain activity using an electroencephalogram (EEG). The subjects were made to gaze at LCD monitor screens at different angles. The researchers analysed the eye movements of the subjects using microsaccade analysis, and the eye positions using an eye-tracking system.

Data and statistical analysis of the study revealed that two types of gamma waves were generated in the primary visual cortex - part of the brain that receives visual input from the retina - in both monkeys and humans. The first type of gamma waves had a frequency of 25-45 Hz, while the second had a frequency of 45-70 Hz. The two types of gamma waves were found to be dependent on the size, orientation, velocity and contrast of the images displayed on the screen.

The researchers also observed an interesting phenomenon - the size of the LCD screen affected the speed of the gamma waves generated. While both types of gamma waves were found when the visual stimulus was big and small, the researchers saw that low-frequency gamma waves were weak with smaller objects, and their presence was felt strongly when the diameter of the stimuli was increased.

Communication mechanisms

Though scientists have studied gamma waves of the brain in the past, this study is the first to observe a relationship between the size of the visual stimulus and the pattern of gamma waves generated. "Unlike previous studies that have shown a single gamma rhythm in the primate visual cortex, we found that large visual gratings induce two distinct gamma oscillations in both monkey and human electroencephalogram," say the researchers.

So far, studies had shown that gamma waves were found in older brain structures such as the hippocampus (part of the brain that plays a role in memory functions) and the olfactory bulb (part of the brain involved in the sense of smell). This study is the first to show that gamma waves are also found in the primary visual cortex area. The researchers believe that the study of these waves will provide more profound insights regarding the communication mechanisms that occur inside the brain.

When brain waves fluctuate, our brain's capabilities are affected adversely. Sometimes, they could be indicative of neuropsychiatric diseases like autism and schizophrenia and may help in understanding these conditions better. All these findings prove that the grand show occurring in your brain could be, in fact, anything but idle and unproductive.

(The author is with Gubbi Labs, a Bengaluru-based research collective)