Exam 5_ Ch 12. Oscillations

Flashcards covering key vocabulary and concepts related to hippocampal network oscillations, including theta and gamma oscillations, their properties, generation, and associated functions.

Network Oscillations

Fundamental to brain function and serve as a crucial mechanism for coordinating neural activity across various brain regions.

EEG (Electroencephalography)

Non-invasive method of measuring the electrical activity of the brain using electrodes placed on the scalp.

Local Field Potentials (LFPs)

Electrical signals recorded within specific brain regions that reflect the combined electrical activity of a population of neurons.

Theta Waves Frequency Range

5-10 Hz. Appear when a rat is engaged in active motor behavior such as walking or exploratory sniffing, but also during REM sleep.

Type 1 Theta Rhythm

Appears during locomotion and other types of voluntary behavior and during REM sleep, has a frequency usually around 5-8 Hz, and is unaffected by the anticholinergic drug atropine.

Type 2 Theta Rhythm

Appears during immobility and during anesthesia induced by urethane, has a frequency in the 4–7 Hz range, and is eliminated by administration of atropine.

Medial Septum (MS)

Thought to be the rhythm generator (pacemaker) of theta. Cholinergic neurons provide slow depolarization of their target pyramidal cells and basket cell interneurons.

Gamma Rhythms

40-100 Hz. Commonly observed in many brain regions during both waking and sleep states. Heavily involved in synchronizing the firing of neurons.

Slow Gamma

25 to 45 Hz. May be associated with broader, more integrative processing, long range processing of information, and memory retrieval.

• encoding more locations

Fast Gamma

60-100 Hz. Often linked to more localized and precise processing, short range processing of information, and memory encoding.

I-I Models

Network consists of only mutually connected inhibitory interneurons with inhibitory synapses having a time constant provided by GABAA receptors, and sufficient excitatory drive to induce spiking.

• recurrent inhibition

E-I Models (PING)

Based on the reciprocal connections between pools of excitatory pyramidal (P) and inhibitory (I) neurons.

• best models

• pyramidal cells fire excitation (using AMPA receptors) onto interneurons → provides inhibition (using GABAa receptors) = gamma oscillations.

• recurrent inhibition

Phase Precession

The timing of action potentials by individual neurons occurs progressively earlier in relation to the phase of the theta local field potential oscillation with each successive cycle.

• Bursts of firing relative to theta, starts on peak and then moves backwards in theta oscillations.

• precision w/ space & time.

iClicker Q: A major source of input into the hippocampus is from

various sensory areas

iClicker Q: Postsynaptic potentials are generated by

Ligand-gated ion channels

iClicker Q: Synaptic inhibition can be produced by

• chloride influx

• potassium influx

iClicker Q: Acetylcholine binds to which of the following

• Muscarinic receptors

• Nicotinic receptors

iClicker Q: Which of the following may contribute to theta oscillations in the hippocampus?

• Phasic excitatory input from the medial spectrum

• Intrinsic resonance of neural excitability

iClicker Q: Which of the following properties of the medial septum (MS) thea generator has commonality with central pattern generators?

Patterned output driven by excitatory input

iClicker Q: If theta oscillations in a mouse are measured at 5 Hz, and gamma oscillations at 100 Hz, how many gamma cycles can occur during ½ of a theta cycle?

10

iClicker Q: Which of the following may contribute to neural synchrony?

Gap junctions

High pass filter

• low frequency do not go through.

• Only passes high frequencies thru (20 Hz +)

Major mechanism #1 for creating theta

Medial Septum Pacemaker (“Classic Model”)

1. MS binds glutamate = depolarize interneurons.

   • Cl- efflux = Excit CA1 onto EC.

2. interneurons binds GABA = hyperpolarize pyramidal neurons = rythmic IPSPs.

   • AP activity bursts of recurrent inhibition.

   • has delayed rectifier = slow K+ channels.

Major mechanism #2 for creating theta

Intrinsic Properties of Hippocampal Neurons

1. I_h (HCN) - channels activated by hyperpolarization = causes depol + rebound.

   • Slow

2. I_m - channels activated by depol = causes hyperpol.

   • K+ current

• resonance = if stopped = no theta oscillations

Calculate gamma cycles using Hertz

Period (cycles) = 1 / Time (sec)

ex: P = 1 / 5 Hz = 0.2 sec