Limbic System Flashcards
Limbic system
Includes group of cortical and subcortical nuclei found on medial aspect of frontal, parietal + temporal lobe
–> interconnected by cortico-cortical pathways
Limbic cortex in frontal + parietal lobe BLOOD SUPPLY
Anterior cerebral artery
Limbic cortex in temporal lobe BLOOD SUPPLY
Posterior cerebral artery
Limbic cortex in frontal + parietal lobes
Orbito-frontal cortex (sub-callosal area) Cingulate cortex (anterior + posterior)
Limbic cortex in lobe
Parahippocampal cortex
Lies in medial temporal lobe
Limbic system function
Mediates sense of reward
Mediates sense of unhappiness or misery
–> for reward or punishment, need to remember experience
–> limbic system involved in memory processes
–> also involved in learning, as to avoid or do an action again
Limbic system connections
Olfactory system
–> some smells hard wired to pleasurable or unpleasant emotions
Reward circuits
Neuronal circuits that are active when you have the sensation of pleasure, joy, happiness etc.
Anterior cingulate cortex
Activated during experience of pain or feelings of misery or depression
Pain information
Lateral spinothalamic tract –>
a) parabrachial nucleus –> amygdala
b) anterior thalamic nucleus –> ACC + insula –> PFC
Prefrontal cortex activated by ACC to…
“do something” about the pain
Cingulotomy
Cutting (anterior) cingulate gyrus to disrupt fibres passing rostro-caudally through it
–> reduces “emotional distress” of pain
V invasive –> not practical
Orbitofrontal cortex
Anterior part of cingulate merges into here
Associated with behaviour when threat is anticipated –> actions to avoid pain (or injury)
Prolonged pressure to make impossible choices causes extreme stress –> cortisol + adrenaline release –> sense of hopelessness + clinical depression
Obsessive compulsive disorders
Excessive activity in orbito-frontal limbic cortex
Posterior cingulate cortex
Emotional significance + memories
Parahippocampal Gyrus
Acquisition of new memories
Subcortical parts of limbic system
Hippocampus + amygdala
Hippocampus
Medial wall of inferior horn of lateral ventricle
Output fibres from fornix which curves upwards and round the over the top of the 3rd ventricle
Fornix- curves forwards and upwards to lie along the midline just under corpus callosum
Fornices of hippocampus attached together by
Septum pellucidum
Fornix
Anterior end of fornix folds down almost vertically at front of 3rd ventricle + ends up in hypothalamus
Septum reaches down to the anterior pole of hypothalamus
–> group of nuclei known as septal nuclei
Fornix axons end in the septal nuclei + mammillary body of the hypothalamus
Neuronal connections between hippocampus + limbic cortex
Info from cingulate cortex –> parahippocampal gyrus
Parahippocampal gyrus –> hippocampus
Info goes from hippocampus along fornix to mammillary bodies in hypothalamus
Info hypothalamus –> anterior thalamus
Anterior thalamus back to cingulate cortex
Connections in Limbic system loop is called
Papez’s circuit
Hippocampus + memory
Memory’s not stored here
BUT Hippocampus is NEEDED for memory storage
Anterograde amnesia
Loss of ability to store new experiences
Loss of hippocampal function
Failure to transfer new experiences into long term memories
Hippocampus function
Labels new experiences with the place + time they occurred
Enables experience to be properly stored in memory
Kluver-Bucy syndrome
Removal of tips of temporal lobes has dramatic effect on animals’ responses to fearful situations
Abnormalities- psychic blindness, oral tendencies, hypermetamorphesis, altered sexual behaviour, emotional changes
–> lost sense of fear
–> Bilateral removal of amygdala
Amygdala location
Embedded in entorhinal (olfactory) cortex in anterior medial temporal lobe
Electrical stimulation of amygdala
Panic, fear and terror responses
Loss of fear
Removal of amygdala and adjacent temporal cortex
Amygdala function
Activates fight or flight response of symp. NS
Sends commands to hypothalamus, which sends commands to reticular formation –> activates reticulospinal tracts + thus Symp. NS
Receives input from temporal lobe cortex –> says if new stimulus is pleasurable, painful etc –> labels experience so info stored in memory with experience
Amygdala damage
Misinterpretation of hazardous events
–> leads to excessive risk taking, odd relations + financial decisions
Decreases one’s ability to recognise emotion in others –> harder to empathise + conduct normal social relationships
Hippocampus vs Amygdala
Hippo- Labels place + date of new experience
Amygdala- Tells us whether pleasant, unpleasant etc.
Ventral striatum
Accumbens nucleus- adjacent to septal nuclei
Septal nuclei- base of septum pellucidum
Basal nucleus (nucleus of Meynert) - just under septal nuclei
Accumbens nucleus
Anatomically part of brainstem, but functionally part of limbic system
Receives dopaminergic fibres as part of mesolimbic dopamine pathway
Mesolimbic pathway
Set of dopamine neurones that project from brainstem regions next to substantia nigra to accumbens nucleus
Accumbens nucleus function
Involved in initiation + termination of behaviours (motor actions) that activate reward pathways
Dopamine input to accumbens necessary for pleasurable behaviour to take place
Blocking dopamine in accumbens –> stop motor actions involved with addictive behaviours
Dorsal striatum (caudate and putamen)
Involved in selection of actions to take based on cognitive plans created in dorsal frontal cortex
Feeds into motor cortex via globus pallidus + motor thalamus
Ventral striatum (nucleus accumbens)
Involved in selection of actions based on threats or rewards
Feeds into motor system via ventral pallidum + globus pallidus
Striatum require
Activity in dopamine axons from midbrain
