lectures 9 (fear conditioning )

circuits for opiate analgesia (process)

• endogenous opiate neurons release peptides in PAG and dorsal horn of Spinal cord

• opiate drugs can act on recpetors in both of these regions to inhibit the pain pathway and exert their analgeisic effects

what is the most common excitatroyr/ inhibitor cells for CNS and PNS?

what is PAG? (periaqueductal Gray)

• consists of parallel columns taht surround the aqueduct in the midbrain and brainstem

• contaisn neural circuts that perform different fucnts, fight or fligth

  • fight/flight

  • analgesia (opioid and non-op mediated)

  • autonomic changes in heart rate/blood pressure

Dorsal PAG (dPAG) = drives flight responses

ventral PAG (vPAG) = drives freezing responses

PAG internet def

a structure in the midbrain (a part of the brainstem) located in the gray matter surrounding the cerebral aqueduct. It acts as a critical hub connecting higher brain regions with the lower brainstem, and is best known for three core functions:

• Pain Modulation: It is a primary control center for descending pain inhibition. It contains high concentrations of opioid receptors, meaning it can suppress pain signals before they reach the brain

• Fear and Threat Responses: The PAG orchestrates instinctive defensive behaviors like freezing, running away, or fighting when you encounter a threat.

• Autonomic Control: It regulates essential bodily functions, including heart rate, blood pressure, respiration, and bladder control

what is tonically active inhibitory cells

neurons that fire continuously over long periods, constantly releasing inhibitory neurotransmitters to suppress the activity of other cells. They regulate the baseline "noise" in the brain and ensure neural circuits don’t become overactive

1. Tonic vs. Phasic Activity

• Tonically active: These cells fire persistently and steadily, maintaining a continuous, background level of inhibition.

• Phasic: In contrast, phasic cells fire in short, rapid bursts only when triggered by a specific stimulus

what are analgesic effects

the relief of pain. It refers to the ability of a medication or treatment to alleviate pain and discomfort without causing a loss of consciousness, distinguishing it from anesthesia

what is spinothalamic pain pathways

pavlonian fear conditioning

• process. = ppl and animals can be trained to be afraid of cues that predict danger,

1. baseline = tone CS is presented alone, and does not elicit behaviroal fear responses

2. acquisition = tone CS is paired with a footshock US, triggering increase in blood pressure and post shock freezing

3. testing. = tone CS is presented alone, elciits a conditioned increae in blood pressure and freezing (CRs)

what pathway is used to connect auditory info from vPAG and ears = fear conditioned Cs can trigger the freezing response after it has been paired with aversive US?

• auditory and pain pathways

temporal stages in memory

• iconic/echoic memories = the briefiest memroies that store sensory impressions that only last a few secs

• STM , AKA working memroy, last for les than one min, or throughout conscious rehearsal

• intermediate term mems = last for hrs or days

• LTMs = last for months, years, lifeitme

fear extinction

repeated presentation of the CS without the US can cause this

the middle ear

• includes the eardrum (aka tympanic membrane)

• bones — called ossicles

  • malleus

  • incus

  • stapes

amygdala (Beginning of Lecture 10)

latin for almond = BLA almond shape

• the tip of the hippocampus

• MT lobe

• fear center

Anatomy of the Amygdala

• the striatal amygdala - has inhibitory projection neurons, and consists of the central (Ce) and medial (M) nuclei

• the central and M nucleus together are called the extended amyg

the cortical amygdala complex has excitatory projection nuerons, and consists of teh lateral (LA), Basal (B) and accessory basal (AB) nuclei.

• the L and B nuclues together = Basolateral (BLA) amyg

the auditory fear conditioning

def = fear conditioning to an auditory CS,

• need the LA and Ce nuclei of the amyg to learn that a tone predicts a shock

• pretraining lesions of Ce / LA only impair the rats Conditioned freeezing response (CR) to the CS