We are born. We grow. We become adults. And throughout it all, memory builds up the scaffold of our lives. Memory tells us who we are, what we’ve experienced, who and what are our relationships, and our place in the world physically, mentally, spiritually, and emotionally. Then brain injury whacks out the poles that support the cross planks of the scaffold that supports us. Some parts remain up while others collapse to the ground. We attempt to rebuild, but the moment we balance two wooden planks across the metal poles joined together, the metal buckles, the planks fall. We wobble inside this unstable scaffolding. We have no confidence in what we know or who we are. We cannot remember our relationships: who is friend and who is foe. We lose our footing, and our place in the world skids out from under us, skipping and flipping out of sight.
Brain injury damaging memory turns ourselves and our world into a confusing, shifting, unknowable thing.
Theories of memory differ, but the basics are working memory, short term, and long term. In addition, there are two types of memory — recognition and recall — and a compensatory mechanism called “confabulation.” And finally, there’s the familiar déjà vu.
Types of Memory
Working memory is that brief moment you hold something in memory in order to accomplish a task or store a piece of knowledge before you forget and scratch your head as you futilely try to remember what you were doing or reading.
Short-term memory is the temporary storage of a piece of information in a stable state ready to use or act on, like being able to remember and dial a phone number that was just given to you.
Long-term memory is the stable storage of information over a long period of time up to and including a lifetime in a way that’s retrievable and usable. Types of long-term memory include remembering events or people from childhood or a character from a novel who resonated with you or what you did last week at rehab.
Recognition memory activates when you read something you’ve read before and recognize it as familiar. Or you bump into someone you know and memory returns: “Oh, I remember you!” Or you walk into a building you haven’t been in for a long time and remember — that is, recognize — the lay-out and furniture. Recognition memory often remains after brain injury even with severe damage. For a psychological overview, see the Science Direct page. For a neuroscience perspective, see Memory Recollection on Science Direct.
Recall memory is used for straight, out-of-the-blue remembering. “What did you do last week?” is a question that has no markers to activate recognition memory. Instead you have to recall it.
Recall memory is susceptible to damage.
Brain Injury Impacts on Memory
Déjà vu is a related, not-well-understood phenomenon that feels like recognition memory. Déjà vu is a French phrase meaning already seen. It describes a sensation of having seen or experienced something previously. Apparently, epileptic seizures in the temporal lobe can create regular feelings of déjà vu. Given that, it’s reasonable to assume that brain injury in the temporal lobe or on a neural network that weaves through critical areas in the temporal lobe may also result in frequent déjà vu — though it has yet to be studied systematically.
Jamais vu and Presque Vu
There’s an opposite, rarely-discussed phenomenon of jamais vu: never seen. It describes a sensation of having never seen or experienced something you have. Brain injury can result in this happening a lot. The only difference between the phenomenon after brain injury and in the normal population is that with brain injury you may not know you have experienced it before and simply cannot believe that you have.
Presque vu is more colloquially known as tip of the tongue. After brain injury, access to vocabulary vanishes like the proverbial mist in the sun. Words hover just out of reach. Not every now and then but all the time. And it’s quite frustrating, especially for those with brain injury who had a robust vocabulary easily accessible before the injury. See Communication.
“People who confabulate present incorrect memories ranging from ‘subtle alterations to bizarre fabrications,’ and are generally very confident about their recollections . . .”Wikipedia
The seeming opposite of memory loss is creating memories of events that never happened. Confabulation is the brain filling in gaps in a way that feels like a real memory. Confabulation is the brain’s response to the person, in a sense, vanishing from reality for a period of time. For example, you may stare out a window for an hour and have no memory of doing so. You don’t understand how it’s jumped ahead an hour in a second. That kind of experience is so unnerving that your brain may compensate by creating a story that presents itself as a memory of you doing something during that hour. Confabulation could also occur after doing an activity such as taking notes during a phone call. You recall the phone call and taking notes, but although the call really happened, you confabulated taking notes, for example. The problem with confabulation is that you don’t know your brain has created a memory unless you bump up against incontrovertible evidence that you actually lost time or didn’t do an activity you recall.
Although it’s well known that brain injury damages memory, researchers don’t know how it does so, how to predict continuing memory loss or regaining of memory, why there’s variability, etc. These remain areas of study. The one thing we do know is that if you cannot pay attention, you cannot take information in. If you can’t absorb and process information, you won’t have anything stored in your brain, either temporarily or permanently. Nothing stored, nothing to remember.
“While it is obvious that damaging any network will lead to compromised functionality, our quantification of memory decline progression could lead to new metrics for understanding memory impairments in a variety of leading neurodegenerative diseases.”Melanie Weber,* Pedro D. Maia, and J. Nathan Kutz. Estimating Memory Deterioration Rates Following Neurodegeneration and Traumatic Brain Injuries in a Hopfield Network Model. Published online 2017 Nov 9. doi: 10.3389/fnins.2017.00623
We know that without functional working memory and short-term memory, you cannot learn or, if you manage to learn, cannot retain the learning. Learning becomes cyclical. You learn x. You execute your learning of x. You don’t use x for awhile like a day or a week, and so you completely forget how to use x. You now have to relearn all over again x. It’s disheartening and frustrating. It’s also time consuming and energy draining. Unlike relearning before you had a brain injury, after the injury, relearning is literally like learning something new. Prior to brain injury, lessons learned long ago may have vestiges in long-term memory so that relearning is quicker and easier than learning it in the first place. Not true for after brain injury. Relearning is as laborious every time as it was the first time.
Memory in the Brain
Another aspect of memory damage after brain injury that I discovered is what I call black holes. Stable long-term memories from before the brain injury seem to vanish only to reappear a few days or weeks or months or even years later. This may happen once or repeatedly with the same memories or a variety of memories.
A stable memory comprises visual, auditory, spatial, and other aspects. The hippocampus sends the visual aspect of the memory to the visual cortex (occipital lobe), the auditory aspect to the auditory cortex (superior temporal gyrus in the temporal lobe) the spatial aspect to the parietal lobe, and so on. The hippocampus organizes and coordinates these aspects. But over time, they coordinate with each other. That’s consolidation.
Apparently, while the hippocampus is the seat of plastic memories, the cortex stores memories in a stable fashion. The hippocampi are small structures deep in the brain, one in each hemisphere. They activate the various parts of the cortex associated with a particular memory. Over time, the various part of the cortex activate each other and no longer need the hippocampi. At this point, the memory has been consolidated and becomes stable. Researchers discovered that sleep plays a critical role in rehearsing memories in order to consolidate them in the cortex.
This is why childhood memories often resist loss when a person becomes unable to remember things. Damage to one or both of the hippocampi costs a person the ability to remember new information. But what happens when brain injury damages various regions of the cortex? Damaged areas corresponding to long-held stable memories may create those black holes.
Action of Neurostimulation?
Neurostimulation seems to restore the hippocampi and their role in learning. The question then is: When neurostimulation restores function does it regenerate the cortical synapses and neurons corresponding to pre-injury learnt memories in the way they existed at the time of injury? And that’s why the black holes fill back in? And/or does neurostimulation also or only create new neurons and synapses ready to create new stable memories in the cortex? And/or does neurostimulation restore the network that activates stable memories — that, in fact, it was the activation neurons that were damaged not the ones that held the memories?
Whatever the cause of loss, memory cannot work in the absence of attention. You cannot encode anything if you don’t attend to it. Healing attentional difficulties is like peeling an onion. Once you’ve removed the effects of attention deficit and distractability, you can see the true state of memory problems, if any, in what remains. And then treat those.