Mkgrady8 Neuro 3 Limbic System

cortical and subcortical nuclei and tracts; more of a conceptually defined functional entity than an anatomical entity; cortical components= cingulate gyrus, parahippocampal gyrus, hippocampal formation, medial orbital gyrus, others; subcortical components= amygdala, hypothalamus (especially the mammillary bodies), thalamic nuclei (anterior, dorsomedial), septal nucleus, habenula, other structures

positioned deep to UNCUS which is located in the anterior-medial aspect of the parahipposampal gyrus

the entorhinal cortex; the hippocampal formation lies deep to parahippocampal gyrus and comprises the medial aspect of temporal lobe

consolidate short term memory to long term memory for declarative types of memory; regulate behaviors such as visceral and motor responses involved in self defense (fear responses) and reproduction; process olfactory info; regulate autonomic function; sometimes called the visceral brain because of its influence on visceral functions through the autonomic nervous system; the HIPPOCAMPAL FORMATION is particularly important for MEMORY, connections with thalamus and cerebral cortex are used for acquisition and consolidation of memories; the AMYGDALA is particularly important for processing EMOTIONS; limbic system also has connections with olfactory system (emotional reactions to smells, memories evoked by smells); mnemonic= MOVES Memory/Motivation, Olfaction, Visceral function, Emotion, Sex drive; the 5 Fs= Feeding, Fear/Fighting, Family, Forgetting, physical Fellowship; HOME= Homeostasis, Olfaction, Memory, Emotion

bilateral destruction of temporal lobes in monkeys (amygdala and most of hippocampal formation and parahippocampal gyrus); wild monkeys transformed into fearless, timid, placid and unaggressive animals; males became hypersexual and remarkably indiscriminate; increased attention to sensory stimuli, with increased oral activities (if it will fit, it sill end up in their mouth); psychic blindness= incessant examination and reexamination of objects in environment, seem to not remember previous examinations

complex and numerous, many reciprocal projections; limbic structures either directly or indirectly connected to the thalamus; input components of the limbic system= hippocampal formation, amygdala, and prefrontal cortex, receives highly processed sensory info about ongoing experiences from all sensory systems; output components of limbic system (motor)= hypothalamus and septal nuclei project to brainstem autonomic and motor areas via the medial forebrain bundle, anterior cingulate cortex (limbic motor cortex), mediate behavioral expressions of emotional states and other limbic behaviors (facial expressions, food, fear, sex, etc)

located in medial temporal lobe; composed of hippocampus, dentate gyrus, and subiculum; reciprocally connected to the output end of the limbic system (septal area and hypothalamus); part of learning and memory circuit that also involves the hypothalamic mammilary bodies, thalamus, cingulate gyrus (classical circuit of Papez) and entorhinal cortex

temporal components= short term, long term; types= cognitive, motor; location of acquisition, storage/retrieval

prefrontal cortex

declarative memory= remembering events, knowing facts, hippocampus, nearby cortical areas, diencephalon (essentially the circuit of papez); procedural memory= skills and habits (striatum, motor areas of cortex, cerebellum), emotional associations (amygdala), conditioned reflexes (cerebellum) (so all the motory areas)

15-20 secs of a limited amount of info; prefrontal cortex and association cortex

involves cognitive manipulation info; the processing of online info

info is stored for a longer period of time, sometimes indefinitely; no overt limit on how much info can be stored

cingulate gyrus --> entorhinal cortex --> hippocampal formation --fornix--> mammilary bodies of hypothalamus --> anterior thalamic nuclei --> cinguate gyrus; medial temporal cortex (hippocampal formation, entorhinal cortex) and medial diencephalon (mammilary bodies, thalamic anterior nucleus) are critical for generation of declarative memories; lesion at any of these regions leads to the inability to form new long term factual memories (aka complete anterograde amnesia for declarative memories); NEED TO KNOW THIS LOOP start at hippocampus); all ipsilateral

declarative memory is acuqired through processing higher order sensory info in POLYMODAL ASSOCIATION NEOCORTICES (prefrontal, limbic, and parieto-occipital-temporal) --> info is conveyed to ENTORHINAL CORTEX in parahippocampal gyrus --> HIPPOCAMPAL FORMATION (for consolidation of memory) --> back to ENTORHINAL CORTEX --> back to POLYMODAL ASSOCIATION NEOCORTICES (for long term memory); entorhinal cortex (and circle of papez) is a go between for memory consolidation by hippocampal formation and long term memory storage and retrieval by polymodal association neorcortices

the medial temporal-medial diencephalic memory system (circuit of papez) communicates with the polymodal association neocortex memory system predominantly through the entorhinal cortex; circuit of papez= hippocampal formation --> mammillary bodies --> anterior thalamic nucleus --> cingulate gyrus --> entorhinal cortex --> hippocampal formation; hippocampal entorhinal circuit= polymodal association neocortex --> entorhinal cortex --> hippocampal cortex --> entorhinal cortex --> polymodal association neocortex

widespread projections from association neorcortex converge on the hippocampal region; the output of the hippocampus is ultimately directed back to these same neocortical areas

damage to components of the circuit of papez specifically the medial temporal area (hippocampal formation), mammilaary bodies of hypothalamus and medial diencephalon (anterior and mediodordal nuclei of thalamus) leads to anterograde amnesia of declarative memories, retrograde amnesia is only for recent events; hippocampal formation does not store 'old' (years) LTM, that is done in distributed neocortical areas; rather HIPPOCAMPAL FORMATION IF CRITICAL FOR CONSOLIDATION OF STM --> LTM

N.A.= fencing accident caused traumatic damage to mammillary bodies, thalamus, anterior temporal lobe (can't lay down new declarative memories); R.B.= bilateral lesion of hippocampal formation from ischemic glutamatergic excitoxicity following cardia bypass surgery (can't lay down new declarative memories); K.C.= bilateral medial temporal lobe damage (can't lay down new declarative memories); H.M.= bilateral surgical removal of hippocampal formation (can't lay down new declarative memories); retrograde amnesia after damage to circuit of Papez typically includes a few years immediately prior to lesion, anterograde amnesia is form time of lesion forward; these pts CAN still create motor memories (can lead to do tasks)

surgical removal of bilateral medial temporal lobes including anterior hippocampus, amygdala, and rostral temporal lobe (e.g. entorhinal cortex); resolved seizure disorder but H.M. lost ability to consolidate declarative STM into LTM; IQ procedural memory and LTM were spared (lost a few yrs of retrograde declarative memory)

LEFT TEMPORAL LOBE= VERBAL DECLARATIVE MEMROY (there are extensive inputs to hippocampal formation from language areas), left temporal lesions --> impaired memory for verbal material; RIGHT TEMPORAL LOBE = VISUAL SPATIAL (NON VERBAL) DECLARATIVE MEMORY, right temporal lesions --> impaired memory for non verbal material such as drawings and music

Receives sensory inputs from all sensory modalities, and organizes appropriate behavioral responses to environmental stimuli, such as context-dependent aggressive vs. non-aggressive behaviors, and social behaviors; Behaviors associated with amygdala function include aggression, fear, sexual behavior and eating; The amygdala is an integral component of CNS emotional circuits and the control of emotional behaviors, including emotional learning and fear conditioning (involves long-term memory consolidation)

Damage to the amygdala interferes with acquisition of memories that are strengthened by emotion and impairs acquisition and expression of Pavlovian fear conditioning, a form of classical conditioning of emotional responses; Important for generating many fear responses such as defensive behavior (freezing or escape responses), autonomic nervous system responses (changes in blood pressure and heart rate/tachycardia), neuroendocrine responses (stress-hormone release); Involved in mediating effects of emotional arousal on strength of memory for the event; Electrical stimulation of amygdala in experimental animals elicits fear or rage; Bilateral lesions of amygdala results in animals becoming placid, and they do not display reactions of fear, rage, or aggression (part of Kluver-Bucy syndrome); Patient S.M. with bilateral amygdalae lesion (due to extremely rare genetic condition known as Urbach–Wiethe disease) experiences no fear or anxiety (despite many traumatic and life-threatening encounters). S.N. is also incapable of recognizing fear in facial expressions of other people and lacks sense of personal space. See Box 29D in Purves for more information about S.M.

behaviors occur in case studies that involved bilateral damage localized to amygdala; The patient displayed marked behavioral changes including visual agnosia, hypersexuality, hyperorality, a tendency to react to every visual stimulus, and memory deficits. The cluster of neurobehavioral symptoms is similar to previously reported accounts of Klüver-Bucy syndrome and suggests the importance of bilateral amygdala involvement in these behavioral changes

mainly amygdala, hypothalamus, and association cortex involved; amygdala involved in autonomic (visceral) functions and the expression of behaviors and emotionally driven movements

Addiction to drugs of abuse (and other reinforcing behaviors, e.g., sex, food, etc.) reflects the susceptibility of emotional neural circuits to dysregulation; These circuits normally serve to provide emotional processing to signal the presence or of prospect for reward and punishment, as well as promoting the activation of motor programs aimed at procuring beneficial rewards and avoiding punishment; Ventral tegmental area in midbrain releases dopamine into nucleus accumbens. This "reward circuitry"is a focal point for addictions to drugs of abuse that PROMOTE DOPAMINE RELEASE IN THE NUCLEUS ACCUMBENS (of basal ganglia) (heroin, cocaine, amphetamines, etc.), essentially pharmacologically short-circuiting limbic circuitry designed to reinforce behaviors that promote emotional satisfaction and behaviors that promote limbic behaviors; amygdala, hippocampus, orbitofrontal, anterior cingulate, temporal cortex --> ventral striatum (nulceus accumbens) --> ventral pallidum, SNpr, mediodorsal nucleus of thalamus

Alterations in limbic function alters much of what is considered to comprise our "human-ness"; MOVES; 5 F's; HOPE

C fearful reactions

B

A