MARIJUANA'S HIGH TIMES NOT MEMORABLE WITH NEURONS OUT OF SYNC

Marijuana--and its active ingredient, delta 9-tetrahydrocannabinol
(THC)--has muddled memories for millennia.

But how exactly the wacky weed interferes with remembrance of things
past--as well as attention span and speech, among other things--has
never been clear.

Now neuroscientists have discovered that cannabinoids diminish the
brain waves of rats--and disrupt the symphony of synchronous brain
cell firing that may be essential for memory.

Neuroscientist David Robbe of Rutgers University and his colleagues
tested the impact of THC and a synthetic cannabinoid on rats that had
their heads restrained. The drugs affected certain brain waves: the
theta (four to 12 hertz) and fast ripple (100 to 200 hertz) waves
diminished significantly, whereas the drug had a slightly lesser
impact on gamma (30 to 80 hertz) waves.

Because theta and gamma oscillations are thought to play a critical
role in creating and storing short-term memories--and fast ripple
oscillations may allow such short-term memories to be moved into
long-term storage--this suppression could mean missing memories for
the rats.

In fact, rats that had been trained to follow a specific series of
turns to get water--and did fine on the test before being
intravenously injected with the drug--found themselves wandering in a
daze under its influence. And when the researchers injected the
synthetic cannabinoid directly into three rats' brains, it completely
disrupted the otherwise synchronized pattern of the firing of their
neurons: they fired as much as before, but in a more random pattern.

And other types of brain cells, such as interneurons and pyramidal
cells, fell out of step as well, although, interestingly, their
overall activity actually increased (perhaps an explanation for the
random nature of thoughts generated by use of the drug).

The finding suggests that this disruption of synchronized brain cell
firing might be responsible for marijuana's memory distortions.
"Overall, our findings indicate that under the influence of
cannabinoids, neurons are liberated from population control," the
researchers write in the paper presenting the finding published in the
December issue of Nature Neuroscience. This, they argue, is the direct
cause of memory impairment. But the research also reveals that at the
highest doses of synthetic cannabinoid, the rats failed to discover
the right sequence of turns altogether. In other words, there may be a
threshold level of the drug that entirely prohibits learning, and that
is something worth remembering very clearly.