The right hemisphere (RH) is our artistic half and is used when drawing, imagining, and dealing with shapes. The left hemisphere (LH) is our logical half and is used during verbal communication, writing, counting, and dealing with sequences. Also, the RH is connected to our left eye and hand while the LH is connected to our right eye and hand. The two hemispheres of our brains are linked by the corpus callosum, through which they communicate and coordinate.

In 1953 surgery was performed on a patient known as HM to relieve the symptoms of severe epileptic seizures. The operation involved removing a large part of the hippocampus. This controlled the seizures but it also produced a severe memory loss. From the time HM woke up from the operation he was unable to lay down conscious memories. Day-to-day events remained in his mind for only a few seconds or minutes. When he met someone he could not recognize them no matter how many times they have met before. HM also believed himself to be a young man right into his eighties because the years since his operation did not effectively exist for him. His case shows how essential the hippocampus is for our memory.

Although the Hippocampus is used to lay down our memories, memory is stored throughout the brain by the neurons that created them. Groups of neurons in the visual cortex will encode a sight and neurons in the amygdala will store an emotion. The hippocampus pulls them all together. The simultaneous firing of all these groups constructs the memory in its entirety.

The initial perception of an experience is generated by a subset of neurons firing together. Synchronous firing makes the neurons involved more inclined to fire together again in the future which recreates the original experience. If the same neurons fire together often they eventually become permanently sensitized to each other, so that if one fires the others do as well.

1 INPUT
An external stimulus triggers two neurons to fire simultaneously. In future, if one fires, the other is likely to fire too.

2 CIRCUIT FORMATION
A third neuron fires. One of the initial pair is stimulated to fire with it, triggering the second, so the three become linked.

3 INCREASING ACTIVITY
The three neurons are now sensitized to one another, so that if one fires, the other two are likely to fire as well.

We have evolved a conscious emotional system but we retain the primitive, automatic emotional responses. A frightening sight or sound registers in the amygdala before we are even conscious of it. While the sensory information is sent to the cortex to be made conscious, the amygdala is already sending messages to the hypothalamus, which triggers changes that ready the body a physical reaction. This allows us to take instant action to save ourselves instead of waiting for instructions from our conscious mind. When we are startled by a loud noise, then relax after realizing it is harmless, we are experiencing both stages - the unconscious reaction followed by the conscious response.

Limbic system structures next to the amygdala are involved in feelings of pleasure, mainly by reducing activity in the amygdala and in cortical areas concerned with anxiety.