US scientists have developed a tool that, for the first time, monitors live brain activity down to the cellular level.
Scientists should get a closer look at the brain in the future
It could be used to tell scientists exactly how drugs affect specific neurons involved in psychiatric disorders, say its creators.
Dr Alison Barth and colleagues at Carnegie Mellon University hope this, in turn, could lead to new treatments.
Their findings appear in the Journal of Neuroscience.
Scientists have mapped general areas of the brain that perform certain tasks, such as memory, behaviour and perception.
However, they have not been able to pinpoint individual nerve cells, or neurons, according to Dr Barth, assistant professor of biological sciences at the university's Mellon College of Science.
To try to overcome this limitation, Dr Barth experimented on mice.
She changed the genes of the mice so a fluorescent protein would light up whenever a particular nerve cell was activated.
In this way, researchers would be able to tell when a drug or a trigger from the environment was acting on a specific neuron by looking for the glow from the fluorescent protein.
Using this technique, Dr Barth was able to identify the precise area of the mouse brain, down to the cellular level, involved in processing sensory information from a single whisker.
This is the first time that scientists have been able to show changes in the activity of nerve cells in response to a sensory trigger in living animals, she said.
"Our transgenic mouse is a novel tool that can be used to visualise, in living brain tissue, a single neuron that has been activated in response to an animal's experience," said Dr Barth.
She has now patented the mouse and licensed it commercially.
She hopes that it will help scientists find new drugs for psychiatric conditions such as schizophrenia.
Dr Barth said: "If you look at a condition like anxiety, for example, when you make a person anxious there are particular neurons that respond to that feeling but it's not necessarily that all of the cells are responding in the same way.
"There may be some cells that are responding much more and the activity of those cells is much more important than the activity of others.
"What this tool does is it allows you to find the cells that are most altered by the state and then you can define the properties of these neurons and design drugs to target those specific cells," she said.
Professor Tony Harmar, professor of molecular pharmacology at the University of Edinburgh, said: "It does look interesting.
"It's the first time this particular technique has been done in animals as far as I know."
He said it was beneficial to know what is going on in living animals because in previous studies the findings were based on postmortem examinations.
"This shows you which cells are doing something while they are alive and that potentially means you can work on the properties of those cells while they are living and that's definitely important.
But he questioned whether it would be possible to look at cells deeper within the brain.
"The cells they looked at were right on the surface so you can easily see them without burrowing inside the brain," he said.
Marjorie Wallace, mental health charity SANE's chief executive, said: "The trouble with drugs used in psychiatry is that we are working in the dark.
"This research could shed light on the links between their chemistry and function in the brain.
"Only by understanding how treatments work will we be able to target medications to individuals and make the drugs of the future safer, more effective and with fewer unpleasant side effects."