According to a study published in October 2011 in Science, a new brain pathway that allows our brain to connect events that happen close together, and plays a role in memory, has been discovered.
Dr. Junghyup Suh from the Massachusetts Institute of Technology led the team of researchers who discovered the link between the hippocampus areas of the brain with the entorhinal cortex. The entorhinal cortex (EC) is located near the medial temporal lobe of the brain and functions as the hub, or central port of navigating memory from all areas of the brain back to the hippocampus. It is the main terminal between the hippocampus and the neocortex — involved in higher functions such as language, sensory perception, conscious thought, motor commands, and spatial reasoning.
The EC plays an important role in autobiographical memory, declarative and episodic memories and in particular spatial memories, including the formation and consolidating of memory and memory optimization during sleep. The EC is also responsible for the pre-processing (familiarity) of the signals in the association of impulses from the eye and the ear.
In order to test their theory the researchers used a mutant strain of specifically bred mice. Removing doxycycline from the food they were fed disabled the cells in the entorhinal cortex of the mice.
Normal mice, when shocked 20 seconds after they heard a sound, learned to associate the sound with the shock and froze in their tracks as soon as they heard the noise. The mutant mice, however, were less likely to react to the sound. When the researchers administered the shock at the same time as the sound, both set of mice behaved the same. This indicates there is a connection between time and the entorhinal cortex.
Another experiment consisted of a water maze and a small platform. The mice would swim around in the water and then rest on the platform. Thirty seconds after they found the platform they were placed in the water maze. The mutant mice were less likely to find the platform again, even though they were there just 30 seconds earlier. Linking the memories of what was currently happening seemed to be more difficult for the mutant mice.
Patients with Alzheimer’s disease have difficulty with memory. According to research, the entorhinal cortex is one of the first areas of the brain damaged in the disease. This research indicates that the entorhinal cortex and its communication to the hippocampus are critical in the formation and retention of memory.
Sources:
Medical Press — Brain circuits connected with memory discovered: http://medicalxpress.com/news/2011-11-brain-circuits-memory.html
Wikipedia — Entorhinal cortex: http://en.wikipedia.org/wiki/Entorhinal_cortex
