When the brain forgets to remember

Despite the shield of the thick, tough bone that forms our skulls, the human brain is still frighteningly vulnerable. Sometimes all it takes is one moderately hard knock to interfere with our ability to remember, think and process.

What happens when we can no longer call upon our memory? How does it feel when our central guiding force, our brain, is suddenly struck by debilitating injury? Speaking with Dr. Padma S. Gunaratne, Consultant Neurologist, at The National Hospital of Sri Lanka, MediScene finds out.

What your memory means to you

Memory is a function of the brain that allows us to retain information or to re-access information about previous experiences. You might find that your memory tends to let you down when it comes to names, but is reliable on dates; you might long for better recall when it comes to sitting an exam or wish you could forget a difficult fight with your spouse; but one thing is certain, for better or worse, our memories shape us. Serving as a filing system, an archive of our personal history and our life's experiences, memories help us live - guiding both our choices and our expectations.

The brain itself is an immensely complex organ. The form these memories take - whether they be auditory, visual or even tactile, whether they be immediate, recent or remote - decide how and where they are processed. Specific parts of the brain, like the hippocampus, amygdala and the cerebral cortex, along with several other highly specific structures, are immensely crucial to the way we process, store and access information and memories. Defective functioning of these parts caused by trauma (accidents), infections or by sedative drugs may result in someone forgetting whole chunks of their lives or being forced to relearn simple words or skills like how to use a blender or how to tie their shoes.

Amnesia and its causes

The term amnesia refers to the partial or complete loss of memory. Memories fall into several different categories and often a division is made on the basis of duration.

Thankfully, amnesia generally lasts only a short while (less than 48 hours). What makes it difficult is that within that period, a person is unable to imagine the future since he or she has no past experience upon which to base expectations. The causes of amnesia range from psychological trauma to brain damage caused by a blow to the head.

Memory loss can also be caused by substance abuse, fits, and most commonly by the onset of degenerative diseases like Alzheimer's or dementia. Infections that damage brain tissue, including meningitis, T.B, encephalitis and herpes, can also result in defective memory. These conditions characterized by impaired cognitive functions and the altered level of consciousness need to be differentiated from amnesic syndromes.

There's much more to amnesia than what one sees in the movies. For starters, there are many different types of amnesia. The main types are:

Anterograde Amnesia: In this type of amnesia, a person may have difficulty remembering events that occurred after suffering damage to the head in some form.

Often able to recall events from their childhood or adolescence, they have trouble remembering day to day events. In such cases, patients tend to be alert, function normally and retain normal cognitive functions but the new events contained in the immediate memory are not transferred to the permanent as long term memory. Some with anterograde amnesia may repeatedly ask the same question - not realising that they had already posed it and received an answer only moments ago.

Retrograde Amnesia: As this name suggests, victims of retrograde amnesia are unable to retrieve memories of events occurring prior to having sustained a blow to the head. Sometimes people never remember the seconds leading up to the incident.

Often anterograde and retrograde amnesia co-exist and result from drug effects or damage to the medial temporal part of the brain, especially the hippocampus. An example for this type of a problem would be the inability of a motorcyclist to recall driving his motor bike prior to the head injury nor the time period of the next two days of hospital stay where he had conversations with his family members.

Transient Global Amnesia (TGA): Cases of TGA are transient in nature - lasting for less than 24 hours. However, over the course of a few years, a person might suffer several attacks of TGA. While the cause and the precipitating factors remain unknown, TGA has been observed most commonly in adults over the age of 50. Still able to recall skills like driving or procedures related to work, someone having an episode is able to function quite as usual but is nevertheless unable to recall what they were involved in even an hour ago. The most characteristic feature of TGA is that one is unable to learn anything new in that period.

Hysterical or Psychogenic Amnesia (Dissociative amnesia): Caused by psychological trauma, this type of amnesia works as a defence mechanism. When an individual is overwhelmingly reluctant to cope with psychological trauma - say violent rape or having witnessed the death of a loved one in an accident - the brain simply refuses to remember the events surrounding the distressing incident. Unlike in the case of memories lost to amnesia caused by physical factors, if these memories do not simply return on their own, they can sometimes be retrieved by psychotherapy or hypnosis.

Korsakoff's Psychosis: Caused by thiamine deficiency related to alcohol abuse or long term malnutrition, Korsakoff's Psychosis results in a person's having both anterograde and retrograde amnesia. They have trouble recalling simple incidents, lists of unrelated words, pictures of complex patterns, even as their short term memory remains. As a result, they will often concoct unnecessarily elaborate stories to cover up simple mistakes. Korsakoff's psychosis tends to be a progressive disorder. Usually accompanied by neurological problems, such as uncoordinated movements and loss of feeling in the fingers and toes, its effects are often difficult to reverse - even if the individual in question is willing to stop consumption of alcohol.

Treatment varies widely according to the type of amnesia and the suspected cause. Handling patients on an individual basis, doctors may try drug therapy or advise the patient to simply rest and allow the memory to return spontaneously. Together, therapists and patients can develop simple strategies to cope with memory impairment.