Learning and Memory

Animals begin to learn as soon as they are born.  Horses learn to stand within seconds and to walk within minutes of birth.  Birds learn to migrate and wolves learn their social status within their group.  Learning is a complex innate behavior which is likely controlled by a myriad of genes.  While there is an abundance of information to study, the complexity of the genetic processes behind learning effectively forbids practical research. Therefore, scientists instead focus research on a simpler, but highly related process – memory formation.

Memory formation and learning are two closely linked processes.  It would be impossible to learn without forming new memories.  Memories are thought to be stored by neurons (the building blocks of the brain) located in the hippocampus.  The link between memory and the hippocampus was discovered after observing that patients who had suffered injury to the hippocampus were no longer able to form new memories.

Patients preparing for brain surgery will undergo a procedure called brain-mapping, a process in which electrodes are inserted into the brain to identify regions with vital functions to ensure their preservation during surgery.  Taking advantage of the brain-mapping procedure, scientists have been able to conduct some intriguing studies.  After patients have electrodes (which can be placed with such precision so that it records activity from a single neuron) inserted into the hippocampus, they are shown pictures of random subjects  The patients are asked whether they recognized the subject in each picture.  This study demonstrated that each memory neuron becomes activated in response to a very specific subject.  For instant, a neuron in one of the patients only responded to a picture of Jennifer Aniston.  Another memory cell from a different patient only responded to a picture of Halle Berry.  Moreover, a sketch of the actress, or a string of words contaning her name also triggered its response.  [Quiroga, et al., 2005]. 

Scientists have discovered several genes that affect learning through animal studies.  In one study, fruit flies were trained to associate a specific odor to an electric shock.  This training was done by giving the flies an electric shock whenever the specific odor was presented in a tube.  A trained fruit fly would avoid the tube that contained the specific odor but three types of mutant genes were unable to learn to avoid the odor, which they named -– dunce (too dumb), rutabaga (unable to form memories) and amnesiac (forgetful).    A similar experiment was performed on mice, but instead of mutating genes, scientists used an inhibitor to block signaling between neurons.  This experiment had the same outcome as the fruit flies.  The mice were unable avoid electric shock in the presence of a neuron inhibitor (see video below).  [Pastalkova, et al., 2006]

We are only beginning to understand the mechanisms behind complex behaviors such as learning.  We believe these mechanisms are intricately controlled by a series of genes.  How fascinating is it that a defect in just one gene can entirely disrupt learning!