Researchers at the Medical University of South Carolina reported in Current Biology that the brain uses the same visual fields for mental imagery and vision, but that it makes less precise use of low-level visual fields with mental imagery than with vision.
These findings combine knowledge in the field by refining the methods of studying mental imagination and vision. In the long run, it may apply to mental health disorders that affect mental image, such as post-traumatic stress disorder.
A symptom of PTSD is an intrusive visual reminder of a traumatic event. If the neural function behind these intrusive ideas can be better understood, then better treatments for PTSD can probably be developed.
The study was conducted by a research research team, led by Thomas P. Nasalaris, Ph.D., Associate Professor in the Department of Neuroscience. The findings of the Nasellaris team help answer an age-old question about the connection between mental imagination and vision.
“We know that mental imagery is similar in some ways to vision, but it may not be exactly the same,” explained Nasellaris. “We especially wanted to know in what ways it was different.”
To explore this question, researchers used a form of artificial intelligence from machine learning, known as machine vision, and which uses computers to view and process images.
“There is an artificial system like this brain, a neural network, that synthesizes images,” Nassellaris explained. “It’s like a biological network that synthesizes images.”
The Naselaris team trained this network to view images and then took the next step to visualize computer images. Each part of the network is like a group of neurons in the brain. Each level of a network or neuron has a different function in vision and then mental imagination.
To test the idea that these networks are similar to brain function, researchers performed MRI studies to see which brain regions are activated by mental imagery or vision.
Inside the MRI, participants viewed images on a screen and were also asked to visualize images at various points on the screen. MRI imaging enabled researchers to define which parts of the brain were active or quiet while participants viewed a combination of conscious and non-living objects.
Once these brain regions were mapped, the researchers compared the results of human brain function from computer models.
They found that both computers and human brains function equally. From the retina of the eye to the region of the brain the primary visual cortex and beyond are activated with both vision and mental imagery. However, in mental imagery, activation of the brain from the eye to the visual cortex is less precise, and in a sense, diffuse.
It is similar to neural networks. With computer vision, low-level areas that represent the retina and visual cortex have precise activation.
With mental imagination, this precise activation becomes diffuse. In areas of the brain beyond the visual cortex, activation of the brain or neural network is similar for both vision and mental image. The difference is what is happening in the brain from the retina to the visual cortex.
“When you’re imagining, brain activity is less accurate,” Naselleris said. “It is short of details, which means that the kind of confusion and blurring you experience in your mental imagination has some basis in brain activity.”
Naselleris hopes that these findings and developments in computational neuroscience will lead to a better understanding of mental health issues.
The blurred dream-like state of imagination helps us differentiate between our waking and dreaming moments. In people with PTSD, aggressive images of traumatic events can be debilitating and feel like reality in the moment. By understanding how mental imagery works, scientists can better understand mental illnesses characterized by disruptions in mental illnesses.
“When people actually have aggressive images of traumatic events, such as with PTSD, one way to think of this is mental imagined disease,” Naselleris explained. “There is some system in your brain that prevents you from producing really bright images of painful things.”
A better understanding of how this works in PTSD may provide insight into other mental health problems such as schizophrenia.
One limitation of the study is the ability to recreate mental images compiled by participants throughout the experiment. Methods for the translation of brain activity into observable images of mental images continue to develop.
This study not only explored the neurological basis of visualization and visualization, but also set the stage for research to improve artificial intelligence.
“To what extent the brain is different. What the machine is doing gives you some important clues as to how the brain and the machines are different,” said Nasalaris.