Let's Explore our Memory: Memory Disorders.

So far, our blog-isodes has largely centered on people with normal memories.

But during the last thirty years, some of the most intriguing questions about
human memory have been raised by studies of people with drastic defects in memory functions that are caused by various kinds of damage to the brain (lesion).

Source

Today, we want to look at two of these kinds:

We have in previous blog-isodes mentioned H.M.,(Henry Gustav Molaison) who suffered from anterograde amnesia produced by lesions(brain damage) in the hippocampus and nearby regions of the limbic system.

In the case of H.M. and others like him, the primary deficit is a massive impairment in the ability to store any new information. But their memory for what happened before the injury is often quite good, especially for events that happened a year or two previously.

Since they remember the distant past and experience the immediate present, they are
often aware that there is a large gap in between.

Some of H.M.'s comments give
some idea of what such an amnesic state is like:

Right now, I'm wondering. Have I done or said anything amiss? You see, at this moment everything looks clear to me, but what happened just before? That's what worries me. It's like waking from a dream; I just don't remember. [And on another
occasion]... Every day is alone in itself, whatever enjoyment I've had, and whatever
sorrow I've had.

Interesting Right?

Now some brain injuries may lead to retrograde amnesia (retrograde, in a backward direction) in which the patient suffers a loss of memories for some period
prior to the accident or the stroke.

That period may be relatively brief, perhaps a
matter of days or weeks. But in some cases, the retrograde amnesia covers a much longer span, and may be reckoned in years.

Some retrograde effects often go along with anterograde amnesia.

Thus H.M. has difficulty remembering events that happened one to three years before his operation, but he has perfectly normal memory for those that occurred before then.

What accounts for the loss of memories for events preceding the cerebral injury?

According to some authors, one of the causes is trace consolidation. This is
a hypothetical process by which newly acquired memory traces undergo a gradual change through which they become established (consolidated) ever more
firmly.

This consolidation effect may be on storage. Young traces need time to become more resistant to forgetting, for until then they are as vulnerable as a cement mixture before it has hardened.

The effect may also be on retrieval, like a
newly acquired library book that will be difficult to find until the librarian takes
the time to fill out its card for the catalogue and to file it properly.

Whether retrograde amnesia effects can be explained in this manner is still a
matter of debate.

One trouble is the fact that retrograde amnesia often extends back for several years prior to the injury. If so, consolidation could not explain the deficit unless one assumes, and some authors do, while others don't, that it is an exceedingly drawn-out process that may continue for very long time periods.

The Bus Stops Here for today:

Thank you, friends, for staying with me through these blogisodes. Your thoughts and opinions are always welcome and appreciated. I'd be happy to hear them. We will build on this in tomorrow's blogisode. Until then, stay safe, friends.