Motivation reward? Or frustration?

*Note: Apologies!  I know I usually post 3 times a week but it's been a bit of a trial getting back into the swing of class after spring break.  Not to mention I had a major paper due this week but I will be much more consistent in the future.

At first, I wasn't sure which topic I wanted to discuss as I enter the subject of motivation.  But as I read my Neuroscience: Exploring the Brain, I stumbled across a rather fascinating example of the disconnect between animals studies and application to the human system.

The setup starts with a simple rat test of motivation.  A rat is implanted with electrodes in its brain which, when the animal shows a specific behavior like pressing a lever, it receives a jolt of current in that brain region.  When the electrodes are properly placed, they affect the dopamine pathways between the VTA (ventral tegmental area) and the striatum or prefrontal cortex.

This has long assumed to be a reward pathway due to the behavior of the rats once they learn the trick.  After the rats connect pressing the lever with the stimulation, they will continue to press the lever as much as possible to get that "fix."  It can even get to the extent that the animals with ignore food and water and exhibit only the trained behavior until they collapse from exhaustion.  But what if what the rat is experiencing isn't actually pleasure?

This diagram helps clear up the basic
pathways of dopamine.

Human trials of this nature are (obviously) unexploited.  But the few times that scientists have implanted electrodes into human brains, it has been to deal with disorders like schizophrenia and severe epilepsy.  And when we sample this population, their self stimulation doesn't seem to be providing that orgasmic reward as expected.

The two examples I read describe the observations of Robert Heath on a couple of patients he assisted at Tulane School of Medicine n the 1960s.  One man, when asked what it felt like to self stimulate the  septal area of his forebrain, reported that it was similar to the feeling of building up to an orgasm.  However, when he tried to repeatedly use the stimulation he was left with the frustrated feeling of incompletion.

The other man focused on medial thalamus (though he had other electrodes in different parts of his brain which he could stimulate).  When asked why he repeatedly stimulated this region when it left an irritable sensation, he replied that it was like the feeling of that moment before you recall a memory.  He would continue to self stimulate on the hope that  it would finally dawn on him, though it never did and he was left as frustrated as the first man.

Robert G. Heath of Tulane

Of course, these case studies are no where near perfect.  Both subjects had severe mental discrepancies from the average population.  And the location of their electrode implants are not identical to those found in the rats.   Lastly, it's a very small subject pool shown here.  But we must admit that the experiences of these men leave room for doubt.  Maybe the rat pushing the lever isn't feeling pure euphoria.   Maybe it's just on the cusp and frustratingly can't reach the peak.  We can't be completely sure.