and then just get into a state of ahhhhh -- you know. >> and why that happens is exactly what columbia university neuro scientist carl harp is investigating. >> exhale. >> research subjects in his lab smoke marijuana and then take a variety of cognitive tests. >> effects will be disruption in memory. disruptions in inhibitory con control. they become slower at cognitive functioning. a wide array of things. they are temporary, but pronounced and clear. >> it is slowly becoming clear to scientists what part of the brain is most effected. the prefrontal cortex. >> it is very important for planning, thinking, coordinating behaviors. tons of marijuana receptors in this region. we think that marijuana,