Behavioral Neuroscience

Describe the four “phases” of instinctive behavior

• Appetite: the seeking or wanting of the stimulus

• Consumption: as appetite reaches a threshold, we consume/take or like the stimulus

• Aversion/Satiety: disturbing response to the same stimulus, like feeling full after eating a lot

• Rest: remain in this phase until appetite goes up again

• all 4 phases don’t always exist

Which phase is affected? Obese patient after gastric bypass

consumption (directly) because it decreases the amount of food they’re able to consume and aversion (indirectly) because if they eat too much they will throw up

Which phase is affected? Abstinent heroin addict taking methadone

appetite (directly) because it provides a low, steady stimulus to decrease the appetite

Which phase is affected? Abstinent alcoholic taking disulfiram that makes them ill if they drink alcohol

aversion (directly) because it makes them ill in response to stimuli, increasing their aversion to it

Which phase is affected? Obesity drugs like GLP-1 agonists

targets consumption because they feel like they’ve eaten twice as much and appetite because they don’t feel as hungry

Which phase is affected? Cannabinoid effects on eating

appetite (directly) because it increases desire for palatable foods

How do we measure “appetitive” behavior experimentally?

• Fixed ratio: certain response requirement gets reinforcer

  • consider session length, reinforcer properties (sedative vs stimulant)

  • limit: intertwines appetite and consumption phase

• Progressive ratio

  • gold standard; what most ppl use to talk about motivation

  • increase response requirement with every reinforcer until “break point”

  • limit: intertwines appetite and consumption phase

  • measure of repetitive drive

• Non-reinforced responding/extinction

  • see how long they go; how bad do they want it

  • acute measure of appetitive strength

  • can’t do over and over

what are obstacles to measuring appetitve drive?

• consumption

  • satiety

  • magnitude of reinforcer

  • gastric motility (food)

  • gastric capactiy

• psychomotor properties of drugs

layers of signals that regulate appetite

• pre-ingestive

  • sight, smell, previous experience

• post-ingestive

  • stretch, macronutrients

• energy status

  • leptin, insulin, fat-free mass, fat mass (coordinate between brain, pancreas, liver, gut to regulate energy)

What are the advantages to using C. elegans as a model organism for neuroscience research compared to mice?

• cost-effective and ethical

• facile and rich genetic tools allow for screening almost every gene

• short duration time so experiments can be completed in weeks rather than months

• transparent!! help discover progressive cell death

what neuron responds to salt chemotaxis in C. elegans?

• ASE

• ASEL (left) and ASER (right) have functional asymmetry

  • left mostly senses Cl-

  • right mostly senses Na+

  • left senses presence of salt

  • right senses absence of salt

what are required for salt chemotaxis in C. elegans?

• cyclic nucleotide-gated channels

• guanylyl cyclases

what is salt chemotaxis learning

• Normally, C. elegans is attracted to salt (NaCl) — it will crawl toward higher concentrations on a plate.

• But if the worm experiences salt in the absence of food, it learns to avoid salt the next time.

• Conversely, if it experiences salt with food, it continues to be attracted or even increases its attraction to salt.

This is called associative learning: salt + starvation = bad ➜ avoid; salt + food = good ➜ seek.

salt chemotaxis learning is what form of long term memory

• implicit (procedural) long-term memory bc associative learning

what signaling pathway promotes salt attraction

Gq/DAG/PKC

what signaling pathway inhibits salt attraction

insulin and PI-3K

conserved in mammals

synapse pair that results in turn

ASER(senses both Na/Cl)→AIB

salt chemotaxis learning changes AIB neuron excitability

• activation of AIB causes turning behavior in mock-conditioned or high-salt cultured as worm likes salt

• in NaCl-conditioned or low-salt cultured , starvation induces learned response to avoid high salt; change in AIB neuron activation thru learned response impacts salt-seeking behavior

learning circuits for salt chemotaxis

• The insulin signaling pathway and neuropeptides are involved in encoding the memory.

• Neurons like AIA, AIY, and AIB help integrate sensory input and modulate behavior.

• Plasticity (changes in neuron response over time) allows the worm to remember the association between salt and its internal state (fed/starved).

how does ASER use glutamate to signal to AIB

• Glutamate can:

  • Excite AIB via GLR-1 (depolarization)

    • activated in high salt response

  • Inhibit AIB via AVR-14 (hyperpolarization)

    • active when worms like low salt

• This dual control allows C. elegans to finely tune its behavioral output based on learned salt associations.

What is required for salt chemotaxis learning?

• DAG/PKC-1 and insulin/PI3K

• glutamate and glutamate receptors

• synaptic plasticity

• neuron excitability change

what is learning

change in behavior based on past experiences

what are the types of associative learning?

• classical (pavlovian) conditioning

  • dogs salivate at tone of bell

  • innate; animal has no control over response

• operant conditioning

  • skimmer box

  • animal must perform action; does have control

what is fear? what are the types?

emotional, physiological, and behavioral response to immediate and severe threat

• innate fear: prey fears predator; built in

• learned fear

types of fear learning; cued fear/auditory fear conditioning

• associative learning, classical conditioning

• training phase: put mouse in box with metal grate and play a tone, then shock

• testing phase: put mouse in different context, play tone with no shock, mouses freezes because associates tone with shock

• delay fear conditioning: tone and shock together, independent of dorsal hippocampus

• trace fear conditioning: gap b/w foot shock and tone, width of gap determines difficulty of learning, dependent on hippocampus

• conditioned stimulus: tone

• unconditioned stimulus: shock

• conditioned response: freezing

types of fear learning; contextual fear conditioning

• same training phase as cued fear

• testing phase: put animal in same context as training, immediately freezes without tone

• shock associated with context

• unconditioned stimulus: foot shock

• conditioned stimulus: context

• unconditioned/conditioned response: freezing

stages of fear conditioning

1. fear acquisition: training

2. fear retrieval: contextual or cued fear test

3. extinction acquisition: put in 3rd context, tone no longer associated with shock, animal stops freezing

4. spontaneous recovery: freezing comes back, tells us extinction only suppresses original training

what part of the brain is central to fear?

amygdala

• basolateral amygdala has both excitatory and inhibitory neurons

• central amygdala has only inhibitory neurons

acquisition of cued fear conditioning

• LA is input association area

  • CS (tone) from auditory thalamus/cortex weak activation of LA

  • US (shock) from brainstem strong activation of LA as LTP is formed and synapses are strengthened

retrieval (or expression) of cued fear conditioning

acquisition of contextual fear conditioning

2 steps

1. context encoding: animal must encode context for 20-30 sec before shock to aclimate

2. context conditioning

contextual fear conditioning: neuronal circuits

hippocampus and associated cortices: context encoding

BLA: context conditioning/association

operant conditioning fear learning: active avoidance

• The animal learns to perform an action to prevent or stop an aversive stimulus.

• It's about doing something to avoid the threat.

🧪 Example:

• In a shuttle box, a tone (CS) is played before a shock (US).

• If the animal crosses to the other side during the tone, it avoids the shock.

• This is called two-way active avoidance.

• If the shock starts and the animal moves to escape it, that’s escape learning (related but slightly different).

operant conditioning fear learning: passive avoidance

• The animal inhibits a natural behavior to avoid punishment.

• It's about not doing something that would lead to a bad outcome.

🧪 Example:

• A rat is placed in a box with two compartments: one light, one dark.

• Rats naturally prefer the dark side.

• But: when the rat enters the dark side, it receives a foot shock.

• Over time, the rat learns to stay in the light side — passively avoiding the shock.

spatial navigation and learning strategies in mammals

route-based strategy (egocentric): path-integration

as we become more familiar with environment we switch to map-based strategy (allocentric)

assays of spatial learning

• T maze

  • spontaneous alternation task tests spatial working (within-trial) memory [memory you can actively rely on, short term]

  • can be modified to test spatial reference (between trials, long term) memory

    • break b/w performing tasks, must have punishment/reward to motivate learning

• Radial arm maze

  • to test spatial working memory: reward at end of each arm, measure number of visits until all food retrieved and errors made

  • to test spatial reference memory, reward at end of 3/8 arms, mulitple trials, measure errors made on testing day

  • somehow differentiate one arm from the other

• Morris water maze

  • tests spatial reference memory, must find hidden platform, multiple training trials

  • testing: platform removed, measure amount of time spent in the target quadrant

• Barnes maze

  • terrestrial version of morris water maze bc mice hate water

brain regions and circuits involved in spatial navigation and learning

• perirhinal cortex

• entorhinal cortex

• amygdala

• hippocampus

connections of the hippocampus with entorhinal cortex and intra-hippocampal circuit

1. perforant pathway

2. mossy fiber pathway

3. shaffer-collateral pathway

afferents: from enorhinal cortex

efferents: to entorhinal cortex

behavior is ultimately comprised of

relex responses (arcs)

difference between learning and memory

• learning is the change in behavior that results from acquiring knowledge about the world

  • modifies reflex arcs

• memory is the process by which information is encoded, stored, and later retrieved

neural network theory

• higher order brain function (learning and memory) depends on the interaction among several neural populations in different anatomical brain regions which are linked via complex connectivity circuits

• each brain region participates in different functions and their role changes over time (plasticity)

what region of the brain is critical for forming declarative (explicit) memories

hippocampus

short-term memory

• involve different neural system than long-term memory

• purpose: maintain transient representations of information relevant to immediate goals

• working memory: maintains current, albeit transient, representations of goal-relevant knowledge

  • has stored and rehearsal components

  • low capacity (only 4-7 items compared to unlimited long-term memory

  • subsystems for verbal and visuospatial info are coordinated by executive control processes (attention)

  • active manipulation mediated by the prefrontal cortex (left dorsolateral area)

• short-term memory is selectively transferred to long term memory

long-term memory

• implicit (nondeclarative) memory

  • typically manifested in an automatic manner, with little conscious processing on the part of the subject

  • stores forms of knowledge that are typically acquired without conscious effort and which guide behavior unconsciously

  • different forms give rise to priming, skill learning, habit memory, and conditioning

• explicit (declarative) memory

  • deliberate or conscious retrieval of previous experiences as well as conscious recall of factual knowledge about people, places, and things

  • has episodic and semantic forms

important brain regions in transferring short term to long term memory

medial temporal lobe, including hippocampus

episodic memory processes

at the level of neural circuits:

• encoding: new info attended and linked to existing info in memory (perception)

• storage: neural mechanisms and sites by which memory is retained over time

• consolidation: makes the temporarily stored and still labile information more stable

• retrieval: stored info is recalled; very similar to perception

at cellular level (mostly in hippocampus): LTP/LTD, synaptic plasticity

hippocampal circuits: perforant pathways

Direct pathway: The axons of EC / layer III neurons form synapses on the very distal apical dendrites of CA1 neurons

Indirect, trisynaptic pathway: It is relayed in the hippocampus through axons that project in the mossy fiber pathway and through Schaffer-collaterals to make excitatory synapses on more proximal regions of CA1 pyramidal cell dendrites

these circuits are essential for declarative (explicit) memory

neural mechanisms of memory processes

LTD is needed for behavioral flexibility, it may be necessary not only to prevent LTP saturation, but also as an active participant in memory storage.

semantic memory

•It is typically not associated with the context in which the information was acquired.

•Knowledge is stored in distinct association cortices

•Retrieval depends on prefrontal cortex

•Semantic knowledge is organized according to conceptual primitives, e.g., form and function; different brain regions associated with animals vs. tools

•Because some categories are particularly dependent on information about form (e.g., living things) whereas others depend on knowledge of function (e.g., inanimate things), focal brain damage can result in the loss of memory for particular semantic categories while sparing knowledge of others

role of sleep in learning

• memory consolidation: slow-wave sleeps enhances declarative memory and REM supports procedural and emotional memory

• synaptic homeostasis: synaptic pruning

• neural reorganization

• sleep deprivation impairs learning by increasing pathological synaptic pruning

impact of exercise on learning

Neurobiology of implicit memory processes

Long-term sensitization involves synaptic facilitation (pre-synaptic) and the growth of new synaptic connections.

Changes in chromatin structure and gene expression mediated by the cAMP-PKA-CREB pathway: regulation of histone acetylation by serotonin

Role of cerebellum

Motor learning

implicit memory:priming

Priming: presentation of stimulus influences its subsequent processing

ØPerceptual priming: occurs within a specific sensory modality, it depends on cortical modules that operate on sensory information about the form and structure of words and objects.

ØVisual priming: almost always correlated with decreased activity in higher-order visual (extrastriate) areas of cortex.

•Font-specific priming is a form of visual priming in which the individual is better able to identify a briefly flashed word when the type font is identical to an earlier presentation, compared to identification when the font is different

ØConceptual priming: provides easier access to task-relevant semantic knowledge, correlates with decreased activity in left prefrontal regions

• word stem completion test

  • implicit memory function: the chance that the person will complete the word shown during the study phase is increased

• The right occipital cortex is required for visual priming for words

implicit memory: procedural memory

Learning involves a shift from cognitive to autonomous stages that use different neural pathways

non-associative learning

age-related cognitive decline

many neurons in the brain are spontaneously active, why is this important?

having multiple types of neurons that spontaneously fire/fire at different paces is important for bidirectional regulation

firing patterns vary within

single neurons

could be a burst pattern during hyperpolarization and a tonic pattern during depolarization

has chemical and behaviroal consequences

what is the basal ganglia responsible for?

motor behavior (initiation, learning)

action selection, decision making

motivational processes like reward, habit formation

these functions are very closely related, bordering on inseparable

what is optogenetics?

the combination of optical and molecular strategies to monitor and control designated molecular and cellular activities in living tissues and cells using genetically encoded photosensitive proteins

using light to excite specific cell types

1. piece together genetic construct made of a promoter to drive expression and a gene encoding opsin (light-sensitive ion channel)

2. insert construct into virus

3. inject virus into animal brain; opsin is expressed in targeted neurons

4. insert “optrode:” fibre-optic cable plus electrode

5. laser light of specific wavelength opens ion channel in neurons

6. record electrophysiology and behavioral results

opsins can be excitatory or inhibitory

can be applied both in vivo (behavorial) and ex vivo (in brain slices)

control is important because blue light can be damaging to tissue and can effect results

how can optogenetics be used to trace functional pathways in reward circuitry

by being combined with real-time place preference (light vs. dark room)

what else can optogenetics be combined with?

instrumental conditioning to study brain circuitry (light comes on/press lever, get food)

pros of optogenetics

• spatial control can be acheived thru cell-type specific strategies (Cre recombinase, CRISPR, etc)

• temporal control is superior to other similar technologies like chemogenetics

• genetic ChR2 mice are available as an alternative to virus injections

• many different types of opsins are available (excitatory, inhibitory, optial switches)

• great for mapping the brain and determining whe

cons of optogenetics

• stimulation protocols are limited by the kinetics of the channels, which are slow (5-15 milisec)

• calcium entry into the cell can be a confound and can bypass the need for action potentials

• channel expression can be weak at the terminals

• blue light is absorbed by brain tissue which limits penetration and can cause damage

• expensive and technically challenging to set up(surgeries are usually required, getting blue light into the head takes some work, etc.)

• glitches still need t be worked out (timing issues with cell type specificity, novel constructs need validation)

chemogenetics

• approaches that use genetically engineered receptors to selectively interact with small, normally inert molecule

• addresses the cell type specificity issue

• use DREADDs: designer receptors exclusively activated by designer drugs

• DNA coding for the DREADD abd a fluro tag are inserted into a viral vector

• virus containing the DREADD DNA is injected into a specific brain region where it begins expressing the DREADD as well as the fluor tag

• CNO (inert ligand) is administered and binds to the DREADD to selectively activate or inhibit the brain region

chemogenetics pros

• spatial control can e achieved through cell-type specific strategies (Cre recombinase, CRISPR, etc.)

• many engineered receptors are now available or will be available soon (excitatory, inhibitory, metabolic kinases, etc.)

• systemic administration of CNO means no fiber optics are needed

• site-specific CNO is an option

• treatment for human neuropsychiatric diseases is a more plausible possibility than optogenetics

chemogenetics cons

• stimulation through pharmacology doesn’t necessarily mimic physiology

• temporal control is tethered to pharmacokinetics, is inferior to other similar technologies like optogenetics

• receptor expression can be weak at the terminals

• somewhat challenging to set up (surgeries are still required)

• systemic CNO could disrupt spatial resolution, as single cell types project many places

• the lignds often have solubility issues

• CNO can back-metabolize to clozapine. rut roh!