Understanding the Limbic System and Memory Functions in the Brain

1. Neuro Revision Emily Hodgson

2. Limbic System

4. Cingulate gyrus Fornix Ant. Nucleus of thalamus Mamillary bodies Parahippocampal gryus Hippocampus Entorrhinal cortex R G Tunstall 2014

5. Limbic system • Convenient way of describing anatomically interconnected nuclei and cortical structures • Most nuclei control functions necessary for self and species preservation • Autonomic and endocrine function, particularly in response to emotional stimuli • Motivation and reinforcing behaviours • Memory • Olfactory connections – more important in other species

6. Hippocampus • Hippocampus is involved in memory (formation & recall) & is located in the inferior temporal lobe • Important role in turning short term into long term memory • Connecting emotions, sounds and smells to memories • Anterograde amnesia – no new memory formation. Able to recall long term memories • Also involved in navigation and spatial orientation • L. Memories involving language • R. Memories involving spatial/visuo-spatial tasks

7. Anterograde Amnesia

8. Retrograde amnesia • Loss of memory/ unable to recall events occurring before the accident/event etc • Usually damage to brain other than the hippocampus

9. Different types of memory • Short term - <1hr • Long term • Declarative/explicit – recall of fact/event/knowledge (takes effort) • Implicit/procedural – learned skills (writing, motor, language)

10. Korsakoff’s psychosis • Part of Wernicke-Korsakoff syndrome (Wernicke encephalopathy normally first) • Mamillary and anterior thalamic damage due to thiamine (B1) deficiency • Memory loss • Difficulty acquiring new information or skills • Change in personality • Confabulation – invents events to fill the gaps in memory

11. Cingulate gyrus • Regulate emotion and pain • Directly drive body’s conscious response to unpleasant experiences • Fear and prediction (and avoidance) of negative consequences – important feature of memory • Autonomic area – cardiorespiratory and digestion • Bladder control • Visual searching

12. Cingulate gyrus • Anterior lesions: • Autonomic dysregulation • Emotional disturbances • Posterior lesions: • Memory/cognitive dysfuction

13. Amygdala • Multiple inputs/activators: • Visual & Auditory • Sensory from body • Solitary tract • Olfactory & Limbic system • Hypothalamus

14. Multiple Outputs: • Hypothalamus • Hippocampus • Multiple areas of cortex

15. Controls multiple emotions, responses and systems • Brings about reactions of: • Fear • Anger • Behavioural emotions • Sweating, flight, fright, confrontation, mating • Impulsivity • Sexual behaviour & emotions

16. Stimulation can: • Increase HR & BP • Reduce saliva • Increase GI motility • Cause irritability • Startle easily • Increase muscle tension • Cause pupil dilation

17. Septal nuclei – pleasure • Nucleus accumbens – • Dopamine activated reward centre • Intense sense of well being • Amphetamine and cocaine activate

18. Hypothalamus • Primary output for limbic system • Sexual function, endocrine function, behaviour and autonomic control • Inputs from most of the body (olfaction, viscera, retina) • Internal sensors for temp, osmolality, glucose and sodium conc, hormones

19. Eyes (Visual Fields)