Functional Neuroanatomy of Memory and Impairment after mTBI

Frederick G. Flynn, DO, FAANMedical Director, Traumatic Brain Injury Program

Chief, NeurobehaviorMadigan Healthcare System

The views expressed in this presentation are those of the author and do not reflect the official policy

or position of the United States Army, Department of Defense or the

United States Government

Memory• Short-term– Information held in mind temporarily– Held for seconds unless repeatedly rehearsed– “Working” memory

• Ability to maintain short –term storage of information that is inaccessible in the environment and the processes that keep the information active for later use

– Prefrontal cortex is vital to normal function• Long-term– Ability to learn new information and ability to recall

info after a delay of minutes to hours– Explicit: conscious learning– Implicit: does not require conscious awareness

Memory• Remote– A form of long-term memory– Information learned, consolidated, and stored in

the past months and years – Includes autobiographical, episodic, and semantic

memories previously stored– Retrieval of information is subject to modification

upon recall– Changes in retrieved information are processed as

newly acquired learning for consolidation, storage, and later retrieval

Explicit Memory Processing

• Encoding–New information attended to and

processed when first encountered–Must be strongly encoded in order to be

recalled later–Attention, motivation, emotional valence

and association with previously learned knowledge strengthen encoding

Explicit Memory Processing

• Consolidation– Newly encoded information is altered in order to

make labile memory more stable for long term storage

– Requires long term potentiation (LTP) and expression of genes and protein synthesis within neurons of the hippocampus

– Subsequent structural changes lead to memory stabilization

Explicit Memory Processing

• Storage –Mechanism by which memory is

retained over long periods of time in distributed cortical sites–Has vast capacity compared to working

memory which is very limited

Explicit Memory Processing

• Retrieval– The process that permits the recall and use

of stored information–Brings together different kinds of

information that are stored in separate cortical network sites–Constructive process which is subject to

distortion

Explicit Memory Processing

• Retrieval– Most effective when it occurs in the same context

that the information was originally acquired and in the presence of the same cues that have been available during the learning process

– Dependent on prefrontal cortex as it involves an active effort and strategy

– Critically dependent on short term working memory

– Enhanced by category cues and multiple choice

Other Types of Memory• Metamemory– Judgment of one’s own knowledge of his/her

memory ability• Prospective memory– Ability to recall the details of an event planned

for the future– Two components: • retrospective : remembering the action that needs to

be performed in the future -“who, what, where, and when”• prospective: remembering to actually take the action

when the future time arrives

Other Types of Memory• Source memory– Temporal (“when”) and spatial (“where”) memory

that is associated with the episodic component of memory (“what”)

– In prefrontal lesions the temporal and/or spatial components of memory may be impaired despite the retention of the details for the event

• Associative memory– Attached pieces of information that accompany

the recall of an explicit memory

Working Memory Processing• Central Executive System– Allocation of attentional resources– Planning, coordinating, and scheduling mental

operations– Analysis of optional responses– Selection of cognitive strategies– Ventral lateral area of PFC: stores and maintains

information on line– Dorsal lateral PFC: monitors and manipulates the

allocation of resources– Networks with bilateral parietal and cingulate

cortex to provide substrate for content specific attention to task and motivational drive

Working Memory Processing• Fluid functioning– Linked with novel problem solving– Involves higher degree of demand on the central

executive – V-S > verbal– After injury delayed recovery compared to crystallized

• Crystallized functioning– Retrieval of over learned information– Requires less demand on central executive– Verbal > V-S– After injury recovery is faster than fluid functioning

Working Memory Processing

• Phonological (articulatory) loop– Verbal domain: dominant (left)hemisphere predominance– Recycles and rehearses verbal material automatically– Actively holds rehearsed material in short-term storage– Involves storage component in the posterior parietal area,

a rehearsal component in the frontal speech areas, and an execution component in the prefrontal cortex

– Recruitment of homologus contralateral regions with increasing task demands

– Profoundly impaired in language disorders such as aphasia

Working Memory Processing• Visuospatial sketch pad

– Non-dominant hemisphere (right) involvement– Spatial and object recall components– Spatial: dorsal circuit from occipital-parietal area to dorsal lateral

PFC– Object: ventral circuit from occipital-temporal to ventral PFC– Recruitment of homologous contralateral areas with increased

demands– Fluid processes have higher association with this system– More closely linked with the central executive– Visual memory tasks place greater demand on the central

executive– Takes longer to recover V-S memory than verbal when executive

dysfunction is present

Neurotransmitters in Memory• No single magic pill for memory impairment• Multiple neurotransmitters involved in the memory process• Ach is most well known – cortical hippocampal system• Glutamate – excitatory efferent hippocampal system• Dopamine – most involved in executive functioning

(mesocortical and mesolimbic)– May have specific dose window of optimal function

• Norepinephrine- works with dopamine to enhance selective attention

• GABA – most significant inhibitory crossed homologous hippocampal neurotransmitter

• Serotonin – mood modulator which may serve to enhance working memory functions through improvement in mood

Dr. Kelly will now present those day to day things that may affect

memory and techniques for improving memory