Memory: Patient HM and Memory Modification

Introduction to cognitive neuropsychology

Neuropsychology

The field of neuropsychology is focused on tying brain structures to their function.

Although MRI technology did not exist at the time of patient HM’s neurosurgery, a modern neuropsychologist would characterize in detail the structures of the brian that have been lesioned using MRI and possibly other methods.

They would then perform a comprehensive battery of behavioral taks to precisely charaterize how he is unable to form new memories.

The primary goal of his investigation is to say this brian region is necessary for this function.

This method is important in understanding the brain because it is a causal method. Most other methods in human neuroscience are purely correlational.

For example, if I shown you a picture of a face, and look at all the regions of the brain that are activated, there will be many. Through clever experimental design, we may be able to say that some regions are active for any visual stimulus and that it is really a set of regions in the face network that respond to faces per se. But, using this method, we cannot say whether this network of regions is necessary for face processing.

The only way to casually implicate these regions is in one of two ways: 1) lesion the region to see if face perception is impaired or 2) activate the region to give the illusionary percept of a face.

Human hippocampus in the temporal lobe. Image from Hippocampus anatomy

Cognitive neuropsychology

Cognitive neuropsychologists are not primarily interested in understanding brain structure and function. Rather, their primary focus is on understanding the structure of cognition.

For example, patient HM’s ability to learn the mirror tracing task without memory of learning it, indicates that their is a cognitive dissociation between declarative and non-declarative memory.

Producing the kind of figure below that explains the structure of cognition is the primary aim of a cognitive neuropsychologist.

Dissociation between declarative and non-declarative memory. “Declarative Memory” by Ayesh Perera

Question for the class: In Squire (2009), what are some other examples of cognitive dissociations that were discovered through working with patient HM?

Clive Wearing

Since patient HM, there have been more cases of anterograde amnesia. Clive Wearing is one case with the worst documented case. For a brief look at how he experiences the world, watch the below clip from the BBC’s documentary A Man Without Memory.