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The Brain : Learning and Memory
CHAPTER 1. MEMORIES ARE MADE OF THIS In 1953, Henry Molaison had his hippocampus surgically removed during an operation in the United States to treat his epilepsy. His epilepsy was cured, and Molaison lived a further 55 healthy years. However, after the surgery he was only able to form episodic memories that lasted a matter of minutes; he was completely unable to permanently store new information. As a result, Molaison’s memory became mostly limited to events that occurred years before his surgery, in the distant past. He was, however, still able to improve his performance on various motor tasks, even though he had no memory of ever encountering or practising them. This indicated that although the hippocampus is crucial for laying down memories, it is not the site of permanent memory storage and isn’t needed for motor memories. The study of Henry Molaison was revolutionary because it showed that multiple types of memory existed. We now know that rather than relying on the hippocampus, implicit motor learning occurs in other brain areas – the basal ganglia and cerebellum. LIVING LESSON Henry Molaison is one of the most famous patients in neuroscience. After surviving experimental neurosurgery for seizures, he was left with severely impaired memory and went on to became a living test subject for five decades, until his death in 2008 DID YOU KNOW? Fear Factor THERE'S AN additional aspect to the amygdala’s involvement in memory. The amygdala doesn't just modify the strength and emotional content of memories; it also plays a key role in forming new memories specifically related to fear. Fearful memories are able to be formed after only a few repetitions. This makes ‘fear learning’ a popular way to investigate the mechanisms of memory formation, consolidation and recall. Understanding how the amygdala processes fear is important because of its relevance to post-traumatic stress disorder (PTSD), which affects many of our veterans as well as police, paramedics and others exposed to trauma. Anxiety in learning situations is also likely to involve the amygdala, and may lead to avoidance of particularly challenging or stressful tasks.