As the central control center of our body, the brain must continue at all costs. It is logical that it be surrounded by biological guarantees: a skull bone, a bag of tissue and blood vessels that filter most infectious insects. When neurons start to decline (as some naturally do with age), the brain can even quickly reconnect networks before we find that something is wrong.
But these same safeguards are a huge hurdle for scientists trying to study brain decline – especially dementia. The gray matter fits perfectly to the slow accumulation of abnormal proteins, the origin of several forms of dementia, and lacks the same receptors of pain as the rest of our body. Thus, when a patient begins to forget or have trouble concentrating, cellular damage is already important – and usually irreversible.
To slow down or prevent dementia, scientists will need to be able to detect it before cognitive systems collapse. The current diagnostic tools for Alzheimer's disease, the most common form of dementia, can confirm the accumulation of beta-amyloid or malformed tau, characteristic of the disease. But they are both expensive (PET) and painfully invasive (dorsal). Blood tests are a promising strategy, although after years of research, scientists are still struggling to distinguish the chemical signs of normal aging from signs of dementia.
Thus, a smaller group of researchers are trying a new strategy. Instead, they turn to changes in our vision – a complex sense with multiple processing steps, each offering scientists the opportunity to capture a blip that signals an imminent brain disaster. This research is in its infancy. But with the population of aging adults at risk of dementia increasing every day, this is a crucial exploration pathway.
The eyes have it
The vision requires us to collect information and send it to the brain, where an entire region tries to interpret it in less than 120 milliseconds (paywall) according to some estimates.
The first stop is the eye, especially the retina, which picks up images that the brain interprets. "The retina is a direct extension of your brain," says Sandra Weintraub, a neurologist at the Northwestern University School of Medicine. "He actually has neuronal cells." When something goes wrong in the brain, the retina can reflect this damage while the inflammation damages tiny blood vessels, called capillaries, around its neuronal cells.
Weintraub believes that lower capillary counts may help indicate the first signs of dementia. In April of this year, she and her colleague Amani Fawzi, also an ophthalmologist in Northwestern, published works showing significant differences in retinal blood vessels of individuals with mild cognitive impairment or early Alzheimer's disease and healthy individuals. . People with cognitive impairment had fewer capillaries in their retinas than those who did not have them.
It was a small study: only 32 people in total, half with symptoms of cognitive decline and others in good health. These are not enough data to predict if a person is at the beginning of dementia. To reinforce this research, Weintraub's team will then focus on a larger group of individuals – preferably with a broader age group and at different stages of dementia progression.
Give meaning to the view
In addition to the eye itself, the brain interpretation images could also serve as an indication of brain health. "The eye is not a camera," says Alyssa Brewer, a neuroscientist at the University of California at Irvine. "The brain contains all kinds of information based on the experience and expectations of how things normally look." This tip probably has a changing goal: it's much easier for us to quickly identify our environment, and especially faces. (This is also why we often find faces in objects that are neither human nor even animals.)
Changes in the way our brain interprets the visual world may indicate a greater neurological change. That's why Brewer is studying the visual cortex of the brain, the essence of image processing. In particular, it examines how the regions of the visual cortex are organized into so-called visual field maps. In a small study published in 2014, she and her team used magnetic resonance imaging to compare the visual cortex of a handful of students, healthy older adults and two adults of the same age. it was diagnosed with mild Alzheimer's disease. Although participants with Alzheimer's disease had normal vision, "their cards were completely messy," says Brewer. "We were really surprised by the magnitude of the changes that occurred very early in Alzheimer's disease."
This work measured the visual status quo of the participants. By extension, a way to detect early changes in the visual capacity of the brain would be to challenge the system with a daunting task, such as watching animals on black and white images for a hundredth of a second on the screen.
This is the idea on which the London start-up Cognetivity is betting. In January of this year, their research team published works in the journal Scientific reports on nature showing that their technique could be used in cognitive health assessments in physicians' offices, although they still have to give the necessary authorization for clinical use. Tom Sawyer, CEO of Cognetivity, told Quartz that the company hopes to test larger populations, including people suffering from depression or multiple sclerosis, to identify the subtle changes in visual cognition that are common to patients. neurological conditions.
Although all these tracks are good for better diagnostic tests, they have a common problem: there is too much individual variability in the structure of the eye, the organization of the cortex and visual processing for create a static measure of brain health. for blood pressure. "We do not have enough control over what is" normal "in many ways, even visual," says Brewer.
That said, simpler ways to take snapshots of brain health could help healthcare providers track their patients' progress over time – and report any serious decline in cognitive abilities. Even if these tests did not diagnose a specific form of dementia, they could prompt health care providers to order earlier tests such as PET scans or backpacks for their patients. Having an early diagnosis before their symptoms develop makes it easier for patients and their loved ones to plan the care they will need, and this allows them to enroll in potentially beneficial clinical trials.