Although scientists now know a lot more about attention deficit hyperactivity disorder (ADHD) than they did in recent years, there is still al to more to decipher. ADHD generally refers to inattentive, hyperactive, and impulsive behaviors that affect how a person functions. One aspect of ADHD may also involve oversensitivity, and an inability in the brain to filter distractions and focus.
There are some ADHD treatments that actually boost the activity of certain brain circuits that are thought to control attention. But a new study has suggested that another option may relate to reducing background signals, which can be a kind of distracting noise. This work, which was reported in Nature Neuroscience, has found that in a mouse model, a gene called Homer1 is related to attention span. Scientists found that when the activity of this gene was reduced, brain activity was quieter and there was more focusing ability.
"The gene we found has a striking effect on attention and is relevant to humans," said senior study author Priya Rajasethupathy, head of the Skoler Horbach Family Laboratory of Neural Dynamics and Cognition at Rockefeller University.
Homer1 is already known to play a role in neurotransmission, and it has been loosely associated with attention disorders before, but Homer1 did not seem to be a major player in attention.
In this study, the researchers assessed genetic data from about 200 mice with varied genetic backgrounds. This work eventually revealed that mice that performed better on cognitive assessments tended to have lower Homer1 activity in their prefrontal cortex, which is important to attention. Further work indicated that it could be responsible for as much as 20% of attention variance in mice, which is a very strong impact.
The team also found that different versions of Homer1, known as Homer1a and Ania3, could lead to huge attention differences. There were (naturally) lower levels of the Homer1a and Ania3 variants in mice that performed well on tests of attention.
When the researchers engineered adolescent mice with lower levels of the Homer1a and Ania3 variants, there were significant cognitive changes; the mice became more accurate, faster, and more focused during different behavioral tests. When these changes were made in adult mice, the same changes were not seen. So the effect of Homer1 seems to be very important during a crucial early-life period.
The reductions of Homer1 in neurons of the prefrontal cortex led to higher levels of GABA receptors. These normally act as a kind of brake on neural activity. So activity came in more focused bursts after a quieter baseline, and neurons fired more accurately.
"We were sure that the more attentive mice would have more activity in the prefrontal cortex, not less," said Rajasethupathy. "But it made some sense. Attention is, in part, about blocking everything else out."
Now these researchers have to confirm these findings in humans, and look for ways to possibly apply them as a potential ADHD treatment.
Sources: Rockefeller University, Nature Neuroscience
