2 - Brain Flashcards
striatolimbic reward circuit
- main target for drugs of abuse
reward circuit
- controls hedonic tone, attention, expectancy of reward, disconformation of reward expectancy and incentive motivation
- reinforces survival behaviours (feeding, drinking, sex, social interactions)
- drugs hijack this circuit and elevate pleasure and reward
hedonic tone
trait underlying an individual’s ability to feel pleasure
reward circuit pathway
- descending myelinated pathway from anterior bed nuclei to ventral tegmental area (VTA) pathway
- ascending dopaminergic ventral tegmental area (VTA) to nucleus accumbens (NAc) pathway (feels euphoric)
- GABA/subtance P/enkephalinergic nucleus accumbens (NAc) to ventral pallidium pathway
drugs in nucleus accumbens (NAc)
- all addictive drugs increase dopamine levels in NAc
- different drugs will activate reward at different sites
drugs in NAc examples
- cocaine, amphetamine, ecstasy will interfere with dopamine re-uptake in the NAc
- leads to dopamine release
- nicotine will depolarize VTA dopaminergic neurons
- leads to release of dopamine downstream
- opioids, GHB, benzos, cannabinoids hyperpolarize VTA GABAergic interneurons
- leads to neuron firing more often, therefore dopamine is released more often
nucleus accumbens (NAc) location
basal forebrain striatum
nucleus accumbens (NAc) function
-pleasure centre
- motivation
- cognitive processing of aversion
- reward/reinforcement of drug taking
- translating of emotional stimulus into behaviour and action
nucleus accumbens (NAc) projections
- reciprocal projections with VTA, PFC, amy, hippo, BG
- pleasure, planning, and inhibition of behaviour via PFC, brainstem, BG projections
ventral tegmental area (VA) location
midbrain
ventral tegmental area (VA) function
- cognition
- motivation
- locomotion
- main driver of rewarding feelings
ventral tegmental area (VA) projections
reciprocal projections with NAc, amy, RN, PFC, BG, etc.
prefrontal cortex (PFC) location
frontal lobe but extends into medial regions
prefrontal cortex (PFC) function
- self-awareness
- planning
- problem solving
- leaning
- memory
- executive function
- personality
- decision making
- social behaviour
- dysfunction linked with mental conditions
prefrontal cortex (PFC) projections
- projections to VTA and amy expression of behaviours trained by chronic drug abuse
- reciprocal connections with multiple regions involved with attention, action, and cognition
- integrated in multiple regions
hippocampus location
para-saggital plane, behind amy
hippocampus function
- memory formation
- processing nove/contextual info
- neuronal stem cells suppressed by drugs (affects long-term memory)
hippocampus projections
VTA that modulate plasticity and learning/memory
amygdala function
- emotions (most disabling symptom in addicts)
- learning/memory
- reward
- attention
- associate cues with drug consumption, conditioning, and reinstatement
amygdala projections
disrupted connection with VTA with drug abuse (amy permits emotional regulation, PFC is in charge of decision making)
caudate nucleus (CN) function
- voluntary movement
- learning
- memory
- sleep
- pain
- social behaviour
- drug accumulation due to the ability to bind transporters
caudate nucleus (CN) projections
- VTA, NAc, hippo, amy
- lesions alter chronic effects
locus coeruleus (LC) location
dorsal pons (in front of cerebellum)
locus coeruleus (LC) function
- arousal
- cognition/memory
- sleep/wake
- attention
- emotion
- stress
- regulates withdrawal symptoms
locus coeruleus (LC) projections
- VTA, brainstem, cerebellum, thalamus, hypoth, hippo, amy, BG, cortex, spine
- LC and norepinephrine afferents are modulated by kappa opioid receptor activation
raphe nuclei (RN) location
dorsal medulla oblongata, and multiple nuclei
raphe nuclei (RN) function
regulate mood, emotion, aggression, sleep, anxiety, memory, appetite, pain, and temp.
raphe nuclei (RN) projections
- hypoth, limbic system, brainstem, spine
- nuclei and forebrain projections are targets of alcohol, opioids, MDMA, etc.
- RN to PFC projections have shown that RN is linked in neuropsychiatric disorders (OCD, ADHD, schizo)
VTA to NAc
dopaminergic projections are the core of the reward circuit
euphoria in drugs
lost in time bc of the removal of receptors
PFC inputs
core of anticipation circuits
amy inputs
core of reinstatement/relapse circuits
reinstatement vs relapse
- reinstatement is drug-seeking behaviour
- relapse is returning to drug taking
neuroplasicity
ability of the brain to form new connection, change wiring patterns and establish new pathways
action potential
nerve fires (transmitters released) as dendrites or soma reach their threshold
repeated firing
long-term changes will occur due to molecular signalling and transcriptional changes
goal-directed circuits
- occasional recreational use to impulsive use to habitual compulsive use
- reward-driven changes to goal-driven drug-seeking behaviour
- ventral striatum-to-dorsal striatum-mediated shift in control of-drug-seeking behaviour
dependance and addiction
- not the same, but highly related
- many drugs induce dependence without addiction
- dependance is triggered by tolerance/withdrawl
- addiction is triggered by reward circuit activation
