Amnesia Flashcards
What’s an engram?
memory trace
Why was Karl Lashley skeptical about engrams being located in a particular region of the cerebral cortex?
He trained rats to on a maze and then destroyed different percentages of cortex
At 5-10% the effect was barely noticeable. At 50% loss is total and it will take longer to relearn. The amount of loss was proportional to the amount of brain destroyed and it could be destroyed in any area of the brain.
What were the two principles proposed by Karl Lashley?
Equipotentiality
Mass Action
What is Equipotentiality?
Different regions contribute equivalently to the storage of a memory trace - because damage to any region causes a loss.
What is Mass action?
Memories depend on the collective action of numerous regions - because the greater the cortical territory destroyed, the graver the loss.
What procedure did William Beecher Scoville perform in 1953?
Bilateral hippocampectomy on H.M.
How did Scoville reach the hippocampus?
Bilateral supra-orbital one and on-half inch trephine holes
What lobe is the hippocampus part of?
Limbic lobe
What areas were removed or damaged in HM?
medial temporopolar piriform entorhinal perirhinal parahippocampal cortices subiculum presubiculum parasubiculum amygdala hippocampal fields CA1, CA2, CA3, CA4 Dentate gyrus
What does the hippocampus consist of?
non-six-layered cortex forming the ventromedial edge of the cortical mantle.
How does the hippocampus communicate with high-order neocortical areas?
via the entorhinal cortex. There’s a loop to and from it plays a key role in hippocampal function.
What is the Papez circuit?
hippocampal formation (subiculum) → fornix → mammillary bodies → mammillothalamic tract → anterior thalamic nucleus → cingulum → entorhinal cortex → hippocampal formation.
It was originally thought to be a cornerstone of emotion but was reconceptualized as the limbic system and shown to be prevalent in memory.
What type of problem did HM have?
anterograde amnesia
What experiment showed that HMs memory is the product of poor encoding rather than forgetting?
He and controls were trained on a series of 120 images. He had to be trained much more than the controls (20 sec, 10 sec at a time vs 1 sec), but he could eventually identify the items when presented next to a distractor item. Importantly, later, he did not forget the pairs.
Two training sessions of 10 sec were used instead of one of 20 so they could keep the time between exposure and test lower.
What study shows that patients with anterograde amnesia have intact working memory?
They trained subjects on 10 words and amnesic patients were equal to control for recalling the last two words, the ones still in working memory.
What does working memory exhibited in amnesic patients depend on?
persistent neural activity, a state-based mechanism, like active rehearsal rather than changes in synaptic strength, a weight-based system.
What study helped to show that rehearsal might be involved in their working memory?
HM did better on a Trigram Task (categorical and rehearsable) than on an Ellipse Task, parametric and not rehearsable. Parametric is related to parameters, but the precise definition eludes me.
What is a Trigram Task?
Categorical, Rehearsable, it involves seeing three letters written together and then remembering and locating that pair in a subsequent display of those same three letters in different orders. As the participant does better, the time between target and probe gets longer. HM was good at this.
