the role of the temporal lobe in memory function Flashcards
Henry Molaison (HM)
- HM= most studied patient in history
- severe temporal lobe epilepsy
- surgery reduced seizures but impacted memory
Theories of memory before HM:
in mid 20th century it was perceived that memory function is distributed throughout the cortex.
- Memory thought to be well integrated with perceptual with perceptual and intellectual functions
No region of the brain was believed to be disproportionately dedicated to memory
Models of memory after HM:
studies of HM was a profound forgetfulness, absence of any general intellectual or perceptual deficit, impairment extended to both verbal and non verbal material, affected information acquired through all sensory modalities
Established the principles that memory is a distinct cerebral function
Hm’s surgery
- Bilateral resection of the temporal tissue. Structures removed; amygdala, most of hippocampus, part of parahippocampal area
- Large amounts of temporal lobe missing in post mortem autopsy, lesion in left frontal lobe (may have occurred during surgery); HM had evidence of lesions In temporal lobe, but there were other damages which may have been associated with his functions.
- Medial temporal lobe; sagittal section, medial surface of right hemisphere,
- Hippocampal formation; bilateral view, anterior
Impact of surgery on HM:
hown to have normal attention span, perserved intelligence
Retrograde amnesia: impairment of memories created prior to injury
Anterograde amnesia: impairment for memories created after injury, impairment in learning novel information
HM had a severe anterograde amnesia:
Declarative memory:
conscious access to information learned previously can be split into episodic memory (events) and semantic memory, facts
Procedural memory
nondeclarative, remembering ‘how to’
HM’s declarative memory:
- Declarative memory was severely impaired
- Couldn’t navigate to find his family home
- Unable to recall names or faces of new people
- Remembered that his mother died, but not his uncle
- Language was largely frozen in 1950’s
Could retain verbal information if rehearsed.
Hm’s procedural memory: not impacted
- Procedual memory function continued intact after surgery
- Still able to learn new skills
- Normal performance on procedual memory tasks
Spared ability to learn new perceptual motor skills.
What does HM tell us about memory function:
- mesial temporal love structures are essential for memory function
- Mesial temporal lobe structures more essential for anterograde than retrograde memory
Distinction between declarative and procedural memory
- Mesial temporal lobe structures more essential for anterograde than retrograde memory
long term impact of HM
the extent of HM surgery was only fully understood post surgery: scoville failed to remove the caudal 2cm of hippocampus
The surgery likely damaged the fibers linking the temporal cortex to frontal
There was evidence of a lesion in the frontal lobe.
Memory network connections:
Sensory information desnt to hippocampal formation via association areas for long term storage
- Memories involve reciprocal connections between hippocampal formation and temporal neocortex.
Hippocampus formation:
- Dentate gyrus+ hippocampus + subiculm
Role of hippocampal formation: - hippocampal formation and surrounding structures are essential for consolidating novel information
Role of hippocampal formation:
hippocampal formation and surrounding structures are essneital for consolidating novel information
- Hippocampal formation necessary for relational memory: paired associate learning tasks, required to remember an association between arbitary pieces of information
Principle extended connecters to the temporal lobe
- The role of the temporal lobe is well known three regions beyond the temporal lobe also pays an important role in memory: papez’s circuit, frontal lobes, diencephalon
