Functional Neuroanatomy of Memory and Impairment after mTBI

1. Functional Neuroanatomy of Memory and Impairment after mTBI Frederick G. Flynn, DO, FAAN Medical Director, Traumatic Brain Injury Program Chief, Neurobehavior Madigan Healthcare System

2. 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

3. 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

4. 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

9. 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

10. 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

11. 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

12. 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

13. 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

15. 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

16. 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

19. 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

20. 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

21. 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

22. 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

24. 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

25. Dr. Kelly will now present those day to day things that may affect memory and techniques for improving memory