Alzheimer’s disease is a truly terrifying condition, one that is difficult to detect early and increasingly difficult to treat over time. It's incurable, and there is no single test that can currently give an accurate diagnosis; the ability to identify the condition early would greatly assist physicians in learning how the disease begins and progresses. A new study published in Science hopes to do just that, by looking at the brain’s navigation network.
Although it is not known when the process that causes the characteristic brain cell degeneration, or neurological atrophy, to begin, we know its effects all too well: aggressiveness, paranoia, hallucinations, delusions, problems with linguistic reasoning, hampered mobility, and both short- and long-term memory lapses.
This neurological atrophy reduces the effectiveness of healthy nerve cells (neurons), gradually destroying them over time. In particular, the area associated with processing thoughts – the grey matter – and the region of the brain responsible for memory – the hippocampus – are severely affected.
Last year, the Nobel Prize in Medicine or Physiology was awarded to the researchers who discovered a new component of the brain responsible for navigation: these “grid cells” create mental maps that allow us to navigate through space without any visual clues. The neurons that make up this grid network are located in a triangular pattern within a region of the brain responsible for memory and navigation, the entorhinal cortex. Those who suffer from progressive atrophy of Alzheimer’s are also at a higher risk at having this cortex damaged.
The researchers came up with a hypothesis based on this information: they thought that Alzheimer’s patients’ difficulty in navigating the world around them is a result of the damage to the grid cells in this cortex.
To test this, a selection of people aged 18 to 30 – one group possessing the genetic marker for Alzheimer’s, and one group who did not (the control group) – were asked to navigate a virtual maze while hooked up to an fMRI scanner that monitors brain activity by tracking blood flow. None of the subjects had symptoms of Alzheimer’s. The virtual space contained mountains, grassland and various objects; the subjects were asked to move and collect these objects around the environment in various ways.
Indeed, those with the gene marker displayed far less activity in their neurological “grid network.” This group, compared to the control group, kept to the edges of the virtual world, perhaps finding it more difficult to navigate without visual markers in the middle of the flat grassy area. However, both groups completed the tasks just as well as each other, indicating that those with perhaps less grid cell activity used other parts of their brain to help them.
Either way, this test could be used as a method of early detection of Alzheimer’s, identifying symptoms in patients potentially many decades before the disease begins in earnest.
