cognitive and behavioural neuroscience

year 2

aim of behavioural neuroscience

• examine how the brain facilitates behaviour and cognition

• explain behaviour by studying physiological processes

what is behavioural neuroscience

the study of how the nervous system shapes behaviour

what does the nervous system consist of?

• central nervous system (CNS)

  • consists of brain and spinal cord

• peripheral nervous system (PNS)

  • consists of nerves that allow CNS to communicate with rest of the body

  • e.g. detects stimulus feather and feeds information back

  • includes voluntary (muscle movements) and involuntary (heart)systems

how is the brain described

as a piece of biological or computational machinery

approximately how many neurons does the human brain contain

85 billion neurons, each one connected to 10-15000 other neurons

what is a neuron

it is the signalling unit of the brain

what can neurons do?

• specialised for transmitting and receiving information

• can communicate with each other as well as other cells and other types of tissues

• can carry information from body to brain

neurons four structures

• dendrites

• soma (cell body)

• axons (inside myelin sheath)

• terminal buttons

soma

• cell body

• metabolic centre of the cell

• contains nucleus

dendrites

• branched; attached to soma

• receive and transmit information from other neurons

• does so via synapse on the surface

axon

• long, thin, cylindrical structures

• carries information (action potential) from cell body to terminal buttons

• very rapid speeds (Range: 1-100 meters per second)

• vary in size (micrometers > ~meter[human axon from spinal cord to foot]

terminal buttons

• axon terminals/buds at end of a branch

• communicate with other neurons via synapses formed via these buds

• when action potential reaches axon terminal, can cause the release of chemicals (neurotransmitters)

neurons communication

most neurons use electrical and chemical signals to send messages throughout the brain

• some neurons do not use neurotransmitters, relying on electrical signals to communicate with one another

how are action potentials created?

created when charged particles (ions) slow into the neurons and generate an electrical impulse that can travel from one end of a neuron to another

definition of action potential

action potential is the momentary reversal of membrane potential that is the basic for electrical signalling within neurons

neurons charge

resting neurons : more negative inside (intracellular) compared to outside of cell (extracellular)

neurons resting potential

approximately -70 millivolts

phases of action potential

action potentials - threshold of excitement

-55mV (all-or-nothing)

why is frequency important is action potentials

a weak stimulus tend to trigger less frequent action potentials compared to strong stimulus as all action potentials are the same size.

speed of action potentials

using ion channels to generate action potentials is slow and uses up a lot of energy.

• some responses need to be very quick e.g. reflexes

• signals travel faster down insulated axons - covered with myelin sheath - allows skipping along axon

why do signals travel faster down insulated axons

myelin sheath insulates axons, allowing conducted signals to travel faster than non-myelinated axons.

allows ‘skipping’ along axons

saltatory action

the process of skipping down the axon, saving energy.

• action potentials decreases in size of myelinated sections, saving energy

• action potential regenerates in gaps: nodes of ranvier

these are all stable within action potentials

signal type, signal strength (voltage), signal speed

variable in action potentials

signal frequency

approaches - monitor

monitor brain activity whilst engaging in a specific activity, to establish underlying patterns during behaviour/cognition

approaches - manipulate

manipulate brain systems, and examine the effect of this on behaviour/cognition

types of psychological methods

• cognitive - response times, accuracy

• survey - questionnaires

• observational - eye tracking

Electroencephalography (EEG)

detects electrical activity, and measure the differences in electrodes across the brain

• looks for event related potentials

strengths of EEG

• excellent temporal resolution

  • it can detect changes in brain activity within milliseconds

  • studying speed of brain processes in real time

• non-invasive

  • electrodes sit on scalp; no radiation or strong magnetic fields

weaknesses of EEG

• poor spatial resolution

  • not able to identify specific regions of the brain activity is coming from

• requires many trials, to allow averaging across due to potential noise (eye movements, muscle activity, electrical interference)

functional imaging - fMRI

measures changes in blood flow and blood oxygenation

• measured using hemodynamic response function (peaks 6-8 seconds)

strengths of fMRI

• excellent spatial resolution

  • it can map where in the brain activity is happening to within a few millimetres

• non-invasive

  • no radiation

weaknesses of fMRI

• poor temporal resolution

  • blood flow response (hemodynamic response function) is slow - 6/8 seconds - so unable to capture rapid brain dynamics

• expensive

• sensitive to movement

functional imaging fNIRS

near-infrared light reflects back from the cap, amount of light differs depending on oxygenation of blood

strengths of fNIRS

• non-invasive, quiet

  • suitable for use with developmental populations or individuals not suited for fMRI

• portable and flexible

  • can be used in relatively natural settings (allows movement)

  • reasonably good temporal resolution

  • better than fMRI, not as good as EEG

weaknesses of fNIRS

• Limited spatial resolution

  • limited spatial resolution

    • cannot localize activity (very limited compared to fMRI)

  • Depth

    • no signals from subcortical regions

functional imaging (MEG)

measures magnetic fields produced by electrical activity in the brain to tell us how different brain regions interact dynamically

MEG strengths

• non-invasive

  • suitable for auditory and language studies

• high temporal resolution (sub-millisecond; like EEG)

• good spatial resolution

  • better than EEG - magnetic fields less distorted by skull than electrical fields

MEG weaknesses of MEG

• expensive - requires a magnetically shielded room

• limited depth sensitivity

  • detects activity from cortical surface areas

• participants must remain still (although less restrictive than fMRI)

manipulating brain function goal

discover functions performed by different regions of the brain, by manipulating brain systems, assessing how they are combined to accomplish behaviours/cognition

• infer the function of a region by examining the effect once removed or modulated

disruption of brain function

• experimentally induced lesions - animal models

• naturally occurring lesions - strokes, brain injury

• non-invasive brain stimulation - TMS, tDCS

• body functioning - coffee, drugs

human lesion studies

naturally occurring lesions - strokes, traumatic brain injury, tumours

opportunity for assessing links between specific brain regions and cognitive and/or behavioural outcomes

strengths of human lesion studies

• can indicate causal relationships between brain regions an particular behaviours/cognitive processes

• unique insight into ecologically and clinically relevant contexts

weaknesses of human lesion studies

• variability and individual differences

  • not possible to control for differences in lesions

  • lesions following stroke, traumatic brain injury, and tumours often affect multiple areas

  • hard to specify exact functions

• brain plasticity

  • especially if lesion occurs during early development

transcranial magnetic stimulation (TMS)

small pulses of electricity send magnetic fields to stimulate neurons in target brain region to create short term virtual regions

strengths of TMS

• helps establish casual relationships

  • help establish regions necessary for - rather than just involved in - particular behaviours/cognitive processes

• non-invasive and reversible

  • avoids brain reorganisation

• can be combined with other methods fMRI/EEG to gain complementary insights

weaknesses of TMS

• limited to surface cortical regions

  • cannot reach deep brain structures

• effects can be variable across individuals

emotions definition

emotions are a process, a particular kind of automatic appraisal influenced by our evolutionary and personal past, in which we sense that something important to our welfare is occurring, and a set of psychological changes and emotional behaviours begin to deal with the situation

six basic emotions

• fear

• enjoyment

• anger

• surprise

• disgust

• sadness

possible 7th emotion

contempt

emotion in amygdala

threat detection - triggers fear/anger

emotion in hippocampus

emotional memory - links emotion to memories

emotion in prefrontal cortex

emotion regulation - regulates and reappraises

emotions in hypothalamus

physiological responses - stress etc

emotions in insula

bodily awareness - senses internal body states

emotion expression (self)

• feeling - being afraid

• physiological changes - increased heart rate

• behavioural outcome - fight or flight

emotion recognition (other)

• perception - inferring emotion

• recognition - emotion is fright

• behavioural outcome - check for danger

emotional response consists of three components

• behavioural components

  • muscular movements appropriate to situation (aggressive posture)

• autonomic components

  • quick mobilization of energy to facilitate required movements (increased heart rate)

• hormone components

  • reinforce autonomic response (further increase blood flow to muscles)

electrical stimulation of the hypothalamus produces

autonomic responses associated with fear - increased heart rate/ muscle tension

• does not increase in self reporting experiences of fear

electrical stimulation of the amygdala produces

increased self-reported feelings of fear increase

• the emotion is recognised and labelled by individual (subject experience)

empathy of fear

when healthy humans watch someone else being given a punishment/shock there is increased activity of the amygdala - social learned fear conditioning

ventromedial prefrontal cortex(vmPFC) is involved in

• regulating emotions

• decision making

• processing risk and fear

emotional dysfunction

frustration tolerance, emotional instability, anxiety, irritability

real world competencies

social inappropriateness, occupational status, financial status, planning

vmPFC lesions show

significant correlations between level of emotional dysfunction and impairments in real-world competencies

amygdala is involved in

recognition of danger (fear/aggression)

• critical for fear-processing; likely involved but less critical for other emotions

emotion recognition

• the ability to perceive and identify another persons affective states

• can be from various cues, including face, voice, body - or a combination

how does group setting affect the display of emotions

• alone - smaller, more subtle signs of happiness

• social - explicit, larger signs of happiness

which brain regions support emotional recognition?

• pre-frontal cortex (PFC)

• amygdala

• superior temporal sulcus (STS)

emotion recognition in STS

superior temporal sulcus is argued to be involved in decoding emotional states, particularly of others based on non-verbal cues e.g. body language

affective empathy

sharing another persons emotional state

affective empathy’s key brain regions

anterior insular > awareness of internal emotional states

anterior cingulate cortex > emotional salience, pain empathy

simulation theory

• we create a model of another persons experience in our brains

• automatic activation of neural circuits that would produce corresponding behaviour in us

• key role of mirror neurons

neurodegenerative disorders

• range of conditions that primarily affect neurons

• progressive loss of neuron structure and/or function

neurodegenerative disorders symptoms

symptoms produced by different disorders can vary dramatically

• motor symptoms

• psychological symptoms

• cognitive systems

• seizures

parkinson’s disease - prevalence

• relatively common

• (1-2% people over 65years old)

• (3-4% people over 85years old)

is the result of a loss of dopamine neurons in the midbrain

parkinsons disease - symptoms

largely a motor issue

• muscle rigidity

• akinesia - inability to initiate movement

• bradykinesia - slowness of movement

• gait impairment

• change in handwriting; decreased arm swing

• resting tremor

• cognitive deficits

parkinsons disease - pathology

caused by degeneration of the dopamine secreting neurons of the substantia nigra

substantia nigra

• a structure in the midbrain crucial for motor control

• produces dopamine

• important role in basal ganglia circuit, controlling voluntary movement

parkinsons disease - cure

no current cure

• number of intervention options aimed to treat and alleviate symptoms of parkinsons disease

parkinsons disease - treatment drug therapy

drug therapy

• gold standard approach - provides greatest symptomatic benefit

• drugs reintroduce dopamine to brain - aiming to provide dopamine for basal ganglia circuit(motor movements)

• L-Dopa > key drug used as dopamine replacement agent

  • dopamine agonist

  • metabolize drug into dopamine, in a relatively short period of time to increase overall dopaminergic activity

  • key treatment for early stages

  • can return to normal functioning for a period of time

not suitable for long term treatment

becomes less effective with time as brain habituates to drug

parkinsons disease treatment - deep brain stimulation

deep brain stimulation

• electrodes permanently implanted in the brain

• targeted at sub thalamic nucleus

  • part of the basal ganglia network specifically involved in motor control

• connected to battery packs implanted under skin on chest

• patient can control frequency of current going in

improves motor symptoms and resultant quality of life

works for a relatively long period of time with maintanence

parkinsosn disease treatment - future

genetic treatment

• cause is unknown

• protein processing issue

• gene therapy?

alzheimers disease - prevalence

most common form of dementia

• 530,000 cases in uk

• 10% of people > 65 years old

• 50% of people > 85%