Limbic System: Processing of Rewarding and Aversive Stimuli

Processing of emotional cues and control of goal-directed behaviour. Limbus "border" in Latin. Cortex-like regions within the medial wall of the temporal cortex. 'Paul Broca - first description of limbic lobe in 1878.'

Dorsal border of the limbic lobe

Cingulate cortex

Ventral border of the limbic lobe

Parahipocampal gyrus

James-Lang theory

Emotion is experienced through physiological or internal changes in the body

Cannon-Bard theory

Emotional experience can arise independently of physiological changes; found through severing the sensory inputs to the CNS and finding the presentation of emotions consistent

Papez circuit

The emotion system is synonymous with the limbic system; the precursor theory to the limbic system

Hypothalamus

Acts as a gate between the limbic system and the autonomic nervous system

Dimensional theories of emotion

Emotions may be represented by different features or dimensions, represented by different brain structures or patterns of activity across multiple brain regions

Amygdala

Involved in storage of emotional memories, appetitive conditioning, and necessary for fear conditioning and the extinction of fear; required for relating contextual cues to stimuli

Components of the amygdala

• BLA: Basolateral amygdala

• CEA: Central amygdala

• MEA: Medial amygdala

Central amygdala

Controls autonomic and somatic responses to emotionally relevant stimuli

Basolateral amygdala

Involved in the formation of memories of emotional relevant stimuli; dependent on recognition of external emotion; neurons encode hedonic properties of a taste

Amygdala finding

Amygdala impairment lead to trouble discerning emotions in faces though no impairments in facial recognition

Fear conditioning

Results in responses of fight; somatic response in running; freezing; autonomic arousal; release of adrenocorticotropic hormone

Brain regions in fear response

• Lateral amygdala: Receives conditioning stimuli via the thalamus

• Central amygdala receives signals via the lateral amygdala

• Central grey: Freezing behaviour

• Lateral hypothalamus: Blood pressure

• Periventricular nucleus of the thalamus: Release of hormones

Hippocampus

Required for contextual learning

Molecular basis of fear conditioning

Conditioned stimulus and unconditioned stimulus inputs converge onto the same cells in the lateral amygdala

Blockage of NMDA receptors

In the basolateral amygdala, fear learning is disrupted

Prefrontal areas consisting

• Orbitofrontal cortex

• Insula

• Prelimbic cortex

• Infralimbic cortex

• Anterior cingulate cortex

Cortical areas functioning

Involved in decision-making, stimulus salience, contextual dependencies of relevant stimuli, and tracking of reward probabilities

Nucleus accumbens

Association of cues with rewards, not necessary for the approach to a reward; important for connection neutral stimuli to outcome of appetitive stimuli

Nucleus accumbens shell

Involved in feeding behaviour and responsible for representing value of predicted outcome; assessing value in a risky decision-making task; receives inputs from frontal cortex

Nucleus accumbens core

Pavlovian approach behaviour; receives inputs from frontal cortex and appears to be responsible for representing motivationally relevant events; GABA/neuropeptide; predictive for devaluation

Ventral pallidum

Processes the hedonic value of stimuli; GABA

Orbitofrontal cortex

Involved in value-based decisions; somatic marker hypothesis—decision making is influenced by physiological responses; necessary for outcome devaluation; lesions impair reversal stimulus learning

Cognitive map hypothesis

Orbitofrontal cortex represents abstract maps, proposing ‘hidden states’ to explain deficts in reversal learning and devaluation

Nucleus accumbens core and shell

• Core: Incentive salience of a reward predictive cue

• Shell: Tracking the value of the expected outcome

Ventral striatum

(Nucleus accumbens) ;inputs from limbic structures and the medial wall of the frontal cortex

Dorsomedial striatum

Inputs from associative cortices, dorsolateral prefrontal cortex, lateral orbitofrontal cortex, and anterior insula

Dorsolateral striatum

Inputs from premotor, supplementary motor, and premotor cortex, as well as sensory areas

Limbic branch

• Cortex: Amygdala, hippocampus, vmPFC, and omPFC

• Striatum: Limbic

• Midbrain: Ventral tegmental area

Associative branch

• Cortex: Dorsolateral prefrontal cortex

• Striatum: Associative

• Midbrain: Dorsomedial striatum

Sensorimotor branch

• Cortex: Premotor/motor

• Striatum: Sensorimotor

• Midbrain: Ventrolateral striatum

Orbitofrontal cortex and striatum

Orbitofrontal cortex inactivation disrupts devaluation-sensitivity similar to dorsomedial striatum inactivation

Prevailing view of cortico-striatal function

Cognitive/limbic loops interact with the motor loops of the basal ganglia, controlling or interacting with the motor system