Notes

Hereafter, two important structures of the limbic systems are highlighted: amygdala and hippocampus. The latter is involved in many functions like emotional behaviour and learning.

Specific Functions of Other Parts of the Limbic System Role of the Hippocampus in Learning. Effect of bilateral removal of the Hippocampus Inability to learn. Theoretical Function of the Hippocampus in Learning Without the Hippocampus, consolidation of long-term memories of verbal or symbolic thinking type is poor or does not take place.

Hippocampus It is part of the cortex and seems to be a particularly sensitive region of the brain. Often epileptic seizures start in the Hippocampus and often represents the first region where Alzheimer's disease symptom take place.

• Vulnerable to damage from anoxia, stress and environmental toxins.
• Often is epileptogenic focus.

HM: bilateral removal of Hippocampus

• Unable to lay down new declarative memories.
• Old memories intact.
• No change in intellect.
• No problems with procedural memory.

Amygdala It is made of several nuclei and it is part of the temporal lobe of the brain rather than the cortex. It receives neuronal signals from all portions of the limbic cortex. Because of it multiple connection, it is called the "window" through which the limbic system sees the place in the world. It seems to be one of the gateways that allows sensation and perception to be associated with particular emotional connotations.

Amygdala: Function and Connections

• Highly processed sensory input.
• Widespread outputs to cortex, hippocampus hypothalamus, brainstem.
• Responsible for learning and maintenance of link between a stimulus and its emotional value.
• Stimulation - fear and anxiety, déjà vu.
• Lesion - e.g., Kluver-Bucy syndrome (Lesions have been studied also in primates and humans, which lead to particular symptoms such as the Kluver-Bucy Syndrome, they studied the effects of mescaline on the brain, resulting in lesions of the amygdala).

Effects of Bilateral Removal of the Amygdala - Kluver-Bucy Syndrome

• Placid, flat affect.
• Fearless.
• Inappropriate social and sexual behaviour.
• Hyperoral and overly curious. Amygdala: learning and memory of emotional significance of stimuli.

Overall Function of the Amygdala It is the behavioral awareness areas that operate at a semiconscious level. The amygdala is believed to make the person's behavioral response appropriate for each occasion.

Functional roles

• Hippocampus: learning and declarative memory (memory for facts, events, faces, places, etc.).
• Amygdala: learning and memory of emotional significance stimuli.