Global Brain Activity

What are Brain Rhythms?

1. Rhythmic environment: temperature, day and night, tides…

2. Brain rhythms: sleeping and waking, breathing cycles, steps of walking, stages of night sleep

What is an Electroencephalogram?

How are Small Fields in Pyramidal Cells Generated?

What are the Basic Requirements for Signal Detection?

Basic requirements for signal detection:

1) A whole population of neurons must be active in synchrony to generate a large enough electrical field at the level of the scalp.

2) This population of neurons must be aligned in a parallel orientation so that they summate rather than cancel out.

What is Synchronous Activity?

EEG/ Brain Rhythms Correlate with Pathology and Behavioural States

Four Basic EEG Phenomena

How are Synchronous Rhythms Generated?

Generation of Synchronous Rhythms- One Neuron Oscillator

What are the Functions of Brain Rhythms?

What are the Behavioural Criteria that Classify Sleep?

Behavioural criteria:

• Reduced motor activity

• Decreased response to stimulation

• Stereotypic postures

• Relatively easy reversibility

How are Dolphins Adapted to Predators?

What are the Three Functional States of Sleep?

Summary Scheme of Sleep-wake States

What are the Functions of Sleep and Dreaming?

• Conservation of metabolic energy

• Cognition

• Thermoregulation

• Neural maturation and mental health

Question 1

Imaging Techniques- Structural Imaging

A. Structural imaging: Measures of the spatial configuration of types of tissue in the brain (static maps)

1.Computerised tomography, CT

2.Magnetic resonance imaging, MRI

Imaging Techniques- Functional Imaging

B. Functional imaging: Measures the moment-to-moment variable characteristics of the brain that may be associated with changes in cognitive processing (dynamic maps)

1.Positron emission tomography, PET

2.Functional magnetic resonance imaging, fMRI

Structural Imaging- CT Scans

CT scans

• Based on the amount of X-ray absorption in different types of tissue.

• Bone absorbs the most (the skull appears white), cerebrospinal fluid absorbs the least (the ventricles appear black) and the brain matter is intermediate (grey).

• Used in clinical settings, e.g. to diagnose tumours or identify haemorrhaging or other gross brain anomalies. 

Structural Imaging- MRI

MRI

• 2003 Nobel prize to Sir Peter Mansfield and Paul Lauterbur.

• Completely safe, so people can be scanned many times.

• Provides a much better spatial resolution.

• Provides better discrimination between white and grey matter.

• Can be adapted for detecting the changes in blood oxygenation associated with neural activity (fMRI).

What are the Sequence of Events in the Acquisition of an MRI Scan?

What is the Basic Physiology Underpinning Functional Imaging?

Example of PET Scans

Example of fMRIs

Functional Imaging- PET

PET

• Based on blood volume

• Involves radioactivity (signal depends on radioactive tracer)

• Participants scanned once or few times

• Temporal resolution: 30”

• Effective spatial resolution: 10mm

• Sensitive to the whole brain

• Can use pharmacological tracers

Functional Imaging- fMRI

BOLD) fMRI

• Based on blood oxygen concentration

• No radioactivity (signal depends on deoxyhaemoglobin levels)

• Participants scanned many times

• Temporal resolution: 1-4”

• Spatial resolution: 1mm

• Some brain regions (e.g. near sinuses) are hard to image

How does fMRI Work?

Imaging Techniques Summary