PSYCHOBIOLOGY 2B

Limbic System Brain Structures

Amygdala, Thalamus, Hippocampus, Insula Cortex, Anterior Cingulate Cortex, Prefrontal Cortex

Limbic System Function

The limbic system is involved in regulating emotions, memory processing, and motivation, facilitating behavioral responses to emotional stimuli.

What is in the Peripheral Nervous System

Automatic Nervous System and Somatic Nervous System

Somatic Nervous System

The part of the peripheral nervous system responsible for voluntary movements and reflexes by controlling skeletal muscles. It consists of sensory neurons and motor neurons.

Stages of Brain Development: Neural Induction

The neural tube forms and closes, cells acquire different identities and dimensions and different parts of the brain start to form

Stages of Brain Development: Proliferation

The stage in brain development where neural stem cells rapidly divide to increase the number of neurons and glial cells, forming the foundational structures of the brain. This takes place in the ventricular zone of the developing neural tube.

Stages of Brain Development: Migration

Cells migrate from bottom level towards top level to their final destination in the developing brain, determining the layered structure of the cerebral cortex and other regions. Radial glial cells guide the migration of neurons to their appropriate locations.

Stages of Brain Development: Differentiation

The process where immature neural cells develop into specialized neurons and glial cells, acquiring distinct functions and characteristics necessary for mature brain function. Transplanted immature cells take on characteristic of a new area in the brain they are integrated into, adapting to the specific environment and requirements of that region.

Stages of Brain Development: Synaptogenesis

Neurons grow more axons and dendrites adding synapses

Stages of Brain Development: Cell death/Stabilization

The process where excess neurons are selectively eliminated while synaptic connections are strengthened, ensuring the efficiency and functionality of neural circuits in the mature brain.

Synaptic Rearrangement

The process by which synaptic connections are reorganized in response to experience or environmental changes, refining neural circuits for improved function. This can involve the strengthening of some synapses while weakening or eliminating others. It leaves a more focused pattern of synaptic contact.

First two years of brain development

• Brain volume doubles in first year and reaches 80% adult size by age 2

• Basic structural and functional framework is in place by the second year of life

Childhood brain development

• Brain development after age 2 is characterized mainly by reorganizing and fine tuning major circuits already established

• Rapid postnatal growth of cortical grey matter over the first two years

• Slower growth of cortical white matter throughout childhood and adolescence

Adolescence brain development

• Higher ratio of white matter to grey matter

• Decreased of synaptic connections at dendrites (grey matter)

• Synaptic connections are refined to make space for mature patterns to form

• First this occurs in the occipital and parietal lobes and then in the frontal and temporal lobes

• Increase of axon myelination (white matter) which speeds up the flow of information

• Myelinated nerves can carry impulses up to 100 times faster, created a more streamlined brain

• However, neural connections are still developing, functional connectivity between the PFC and subcortical structures do not reach a stable state until the mid-20s

Balance Model of Brain Development

A theoretical framework that emphasizes the interplay between genetic and environmental factors in brain development, highlighting how both influences shape neural networks throughout different life stages.

• Reward-related subcortical regions and prefrontal control regions interact differently across development

• The motivational and emotional subcortical connections develop earlier than connections supporting prefrontal control

• This results in a greater reliance on motivational subcortical regions than on prefrontal regions during adolescence

 

Effect of Prenatal Tobacco Exposure

• Toxins in tobacco can cross placental barrier

• This can dampen gene expression of regulatory genes responsible for brain growth, myelination and neuronal migration which alters brain structure and function

• Long lasting effects such as risk for psychiatric disorders and addiction

Effects of Prenatal Maternal Stress

• Exposure to increased cortisol increases risk for behavioural and mental health problems layer in life

• It impacts on functional and structural brain connectivity involving amygdala and PFC and hypothalamic pituitary adrenal axis

Effect of Prenatal Maternal Depression

• Associated with elevated maternal cortisol

• Maternal cortisol levels predict larger amygdala in 7 year old children

• Amygdala volume partly mediated association between maternal cortisol and child affective problems

• 6 month olds born to mothers with higher prenatal depressive symptoms showed greater functional connectivity of the amygdala with key regions involved in activation and regulation of emotional states

Effect of Socio-Economic Status

• Higher SES is associated with prolonged structural and functional brain development leading to more efficient cortical networks in adulthood

• For low SES greater exposure to chronic stress seems to accelerate brain maturation

• Prolonged exposure to stress can lead to differences in brain structure and functioning, impacting cognitive and emotional outcomes.

Effect of Poverty

• Poverty affects mental/physical health and life outcomes through toxic stress

• 8-9% reduction in grey matter in frontal and temporal cortex and hippocampus in children/adolescents ages 4-22 living below the poverty line

• Grey matter reductions explained 15-20% of the income related achievement gap

Effect of Neglect

• Neglected children have mean frontal-occipital circumference below the 5th percentile

• Brain size improved when children were removed from neglectful environment and reassessed after 1 year in foster care, especially when younger

Retrogenesis

• Idea that brain structures that mature earlier in development are more robust to effects of ageing compared to structures that mature later

• Grey matter in the prefrontal cortex declines ~5% per decade from age 20 onwards.

• The hippocampal volume also decreases with age which results in a decline in multiple areas of cognition including working memory, episodic memory, processing speed and executive function.

 

HAROLD Model

To compensate for these structural declines, it can use the HAROLD model (Hemispheric Reduction in Older Adults model). This involves increased bilateral recruitment of pre-frontal areas.

The HAROLD model suggests that older adults engage both hemispheres of the brain to compensate for age-related declines, improving cognitive function through bilateral activation.

PASA Model

It can also use the PASA model (Posterior Anterior Shift in Ageing model). This involves recruitment of prefrontal-cortex in response to reduced visual cortex activation.

Self Control Top Down Processing

• Refers to the ability to regulate one's thoughts, emotions, and behaviors through higher-order cognitive processes that involve the prefrontal cortex, enabling goal-directed actions.

• Includes the PFC, Cerebral Cortex and Dorsolateral PFC

Self Control Bottom Up Processing

• Refers to the automatic, reflexive responses to stimuli that arise from the lower brain structures, allowing for immediate reactions without higher cognitive involvement.

• This type of processing often bypasses the prefrontal cortex, relying more on instinctual behavior.

• Brain stem and basal ganglia are involved in this process, including the ventral striatum within the basal ganglia and the nucleus accumbens within the VS

• Limbic System is also involved in this, including Amygdala and Hypothalamus

Balance Model of Self-Control

The idea that behaviour is predicted by the balance of activity in control systems such as the dorsolateral PFC and the reward systems such as the ventral striatum

Cognitive Strategy of Self Control

A method used to enhance self-control by employing cognitive processes to regulate thoughts and actions, often by activating the prefrontal cortex. This can be for example, thinking of negative consequences of smoking in order to reduce cravings. This increases activity in the PFC and decreases activity in the reward centers of the brain, including the ventral striatum, amygdala and ventral tegmental area, influencing decision-making and impulse control.

Smaller-sooner rewards

• When individuals prefer to receive immediate gratification over larger but delayed rewards.

• Predicts higher impulsivity, impatience, poorer school performance and increased risk of substance abuse

• Greater connectivity in the limbic system makes you more likely to choose smaller sooner rewards

Larger-later rewards

• When individuals opt for larger rewards that require delayed gratification, it reflects a capacity for self-control and patience.

• Greater connectivity between cortical regions within cognitive control systems (dorsolateral PFC, dorsal anterior cingulate cortex and superior frontal cortex) makes you more likely to choose larger later rewards

Repetitive Transcranial Magnetic Stimulation (rTMS) on Self Control

• A non-invasive procedure that uses magnetic fields to stimulate nerve cells in the brain.

• Can be used to create a temporary lesion effect at low frequency

• After rTMS, one study showed patients were less patient and preferred smaller-sooner rewards

Transcranial Current Stimulation (tDCS) on Self Control

• A non-invasive brain stimulation technique that places electrodes on the scalp on the cortical regions of interest

• This modifies spontaneous neuronal excitability by changing neurons resting membrane potentials

• When activating the right dlPFC with tDCS twice a day for 5 days, participants made less risky choices, and risk reduction persisted at a 1 and 2 month follow up

• When activating the left dlPFC with tDCS there is improved accuracy and reaction time, perhaps pointing to a more thoughtful, top-down control system

Meditation on Self Control

Increases the activation of the resting state Anterior Cingulate Cortex and Prefrontal Cortex so can alter activity in self-control circuits. Meditation promotes self-regulation and enhances attentional control by strengthening neural connectivity. Regular practice can lead to improved emotional regulation and decision-making abilities.

Adolescent Self-Control

• Inhibitory control stems from childhood, so higher self-control children = higher self-control adults

• Adolescents were thought to take more risks because of an underdeveloped PFC however, children also have this and do not display the same risk-taking

• Adolescents have stronger nucleus accumbens activation to rewards compared to children and adults, which explains increased reward-seeking behaviour in adolescence

• Functional connectivity between the PFC and subcortical structures does not reach a stable state until the mid 20s

• The Imbalance Model explains that self-control during adolescence is influenced by the mismatch of the developing balance between the reward system and the regulatory functions of the prefrontal cortex.

What areas of the brain are involved in social interaction?

• Medial prefrontal cortex

• Temporoparietal junction

• Posterior superior temporal sulcus

• Inferior frontal gyrus

• Interparietal sulcus

• Amygdala

• Anterior cingulate cortex

• Anterior insula

These regions play crucial roles in processing social cues, understanding others' perspectives, and regulating emotional responses during social interactions.

Vicarious Embarrassment

• A social emotion where an individual feels embarrassment on behalf of another person, often arising from witnessing someone else's awkwardness or failure.

• It activates areas associated with empathic concern (ACC), Theory of Mind (middle temporal gyrus) and social identity (inferior frontal gyrus)

The Perception Network

A network of brain regions that processes sensory information and interprets social signals. It plays a vital role in understanding and responding to the emotional states of others.

1. Socially salient stimuli (facial expressions)

2. Activates sensory association areas of the temporal cortex

3. The ventrolateral amygdala and lateral orbitofrontal cortex receive input

4. We can use this information for emotional processing, using past experiences in order to guide social behaviour and interactions.

5. Impaired perceptions of facial expressions and sarcasm comprehension can be attributed to structural differences in the amygdala. lateral orbitofrontal cortex and temporal pole

The Affiliation Network

A network of brain regions involved in forming social bonds, fostering cooperative behavior, and enhancing group cohesion. This network includes areas such as the ventral striatum, anterior cingulate cortex, and lateral prefrontal cortex, which are activated during social interactions and emotional connections.

1. Nuclei in medial amygdala and ventromedial prefrontal cortex connect to subgenual anterior cingulate cortex and ventromedial striatum

2. This is important for processes associated with motivating pro-social behaviour

3. For example, we respond to pictures of loved ones with positive social feedback and behave more altruistically

4. Decreased grey matter in the ventromedial PFC is linked to diminished empathy and interpersonal warmth. This illustrates how brain structures can influence our social motivations and connections.

The Aversion Network

A collection of brain regions associated with the experience of negative emotions, such as fear and disgust. It is crucial for processing aversive stimuli and has implications for understanding anxiety and phobic responses.

1. Nuclei in rostral dorsal amygdala and caudal anterior cingulate cortex connect to pain sensitive targets

2. Regions in this network respond to untrustworthy faces and negative social feedback that elicit social aversion and motivate decisions to not cooperate

3. Frontotemporal dementia patients with atrophy in the network were more willing to trust strangers and fall for scams

Altruistic Choices

Decisions made for the benefit of others, often at a personal cost. These choices reflect a capacity for empathy and social connectivity. They activate areas such as the anterior cingulate cortex, nucleus accumbens and ventromedial PFC, although altruistic choices more strongly activate the subgenual ACC. Altruistic choices give intrinsic satisfaction which relates to the posterior ventromedial PFC

Strategic Choices

Decisions made with consideration of potential outcomes, often involving trade-offs between personal gain and social dynamics. These choices engage brain regions associated with reward processing and social cognition, including the anterior cingulate cortex, nucleus accumbens and ventromedial PFC, although strategic choices more strongly activate the nucleus accumbens. Strategic choices give extrinsic rewards and relate to the anterior ventromedial PFC

Default Mode Network

• Area active when daydreaming

• Includes areas like the medial PFC and temporoparietal junction and is strongly associated with mentalizing, which is the ability to understand and attribute mental states to oneself and others.

• It is also involved in a broader range of social cognitive processes including understanding social interactions, interpreting social cues and forming social judgements

Reward Circuits

Brain pathways involved in the processing of rewards, including the nucleus accumbens, ventral tegmental area, and associated areas that regulate motivation and reinforcement in response to rewarding stimuli.

Sympathetic Nervous System Role in Stress

• Includes the amygdala, hypothalamus, adrenal glands and epinephrine

• Initiates the fight or flight response

• Epinephrine activates physiological changes such as increased heart rate, rapid breathing, relaxed bronchi, more oxygen being sent to the brain, heightened senses and release of blood sugar and fats, preparing the body to respond to potential threats.

Hypothalamic-Pituitary-Adrenal Axis

• Made up of the hypothalamus, anterior pituitary and adrenal cortex

• Hypothalamus releases corticotropin-releasing hormone (CRH)

• This stimulates the pituitary gland to secrete adrenocorticotropic hormone (ACTH)

• This, in turn, prompts the adrenal glands to produce cortisol, influencing stress response and regulation.

Transactional Model of Stress

A framework that describes stress as a process resulting from the interaction between an individual and their environment, emphasizing cognitive appraisal and coping mechanisms. Stress responses are evoked when there is a perceived imbalance between demands and resources available for coping. The stress response depends on how that person appraises an external stressor.

Primary Appraisal of Identity Threats (PAIT)

The initial cognitive evaluation of whether an identity threat is harmful or a challenge, determining how an individual will respond to the stressor.

Secondary Appraisal

The process of evaluating available resources and options for coping with a perceived threat, influencing the individual's response to stress.

Effects of Acute Stress

Can impair PFC function and performance of tasks that require complex, flexible thinking. Working memory is also impaired under stress as it is a part of PFC function and can lead to increased anxiety and fatigue. Acute stress can also enhance amygdala and hippocampus function.

Effects of Chronic Stress: Neuronal remodelling

Chronic stress can trigger neuronal remodeling, decreasing the length of dendrites in the PFC and increasing their length in the amygdala. It can impair immune function due to allostatic overload.

Effect of racial discrimination

• Racial discrimination can lead to chronic stress responses, negatively impacting mental and physical health outcomes. It may also affect cognitive function and overall well-being, contributing to feelings of anxiety and depression.

• When anticipating discrimination, there is a cardiovascular response that causes blood pressure and cortisol to increase

• The anterior cingulate cortex is activated by social exclusion, as it integrates social cues related to complex social experiences

• Higher distress from social exclusion causes higher ACC activity

• Perceived discrimination is associated with activity of pregenual ACC, with a high density of glucocorticoid receptor indicating altered stress processing in individuals effected by racial discrimination.

• Ventral PFC is involved in top down regulation of stress during social rejection, activity is seen to be lower with higher perceived stress.

• This means that racial discrimination activates brain regions involved in social distress and reduces activity in regions involved in emotional regulation.

Effect of PTSD

• PTSD is associated with rapidly assessing salience of threat related stimuli.

• Higher PTSD symptoms cause stronger activation of the amygdala in response to threat.

• PTSD decreases hippocampal volume compared to trauma exposed individuals without PTSD, therefore is not the result of experiencing the trauma itself.

• Hippocampal volume does not increase with successful treatment.

• Smaller hippocampal volume may be a pre-existing condition that may make the brain more vulnerable to developing pathological stress responses.

What is the Suprachiasmatic Nucleus (SCN)

A specialised group of hypothalamic cells that receives information about light exposure from ganglion cells in the retina along the retinohypothalamic tract. This activates melatonin secretion by the pineal gland

Dim Light Melatonin Onset

The time when melatonin levels rise above threshold under dim conditions, which can be measured via saliva or blood

Health Belief Model

A psychological model that explains health behaviors based on individuals' perceived susceptibility and severity, perceived benefits of action, and barriers to action

Theory of Reasoned Action

A theory that predicts individual behavior based on their intention to perform that behavior, which is influenced by attitudes toward the behavior and subjective norms. However mPFC activity predicted behaviour change over and above self reported intentions and attitudes in one study

Theory of Planned Behaviour

An extension of the Theory of Reasoned Action that incorporates perceived behavioral control as an additional factor influencing intentions and behaviors.

Self-Efficacy

• A belief in one's ability to succeed in specific situations or accomplish a task, which can influence motivation and actions towards achieving goals.

• It is associated with increased activation in the rostral medial PFC which is involved in appraisal of negative emotion and self assessment

• It is also associated with increased connectivity between the mPFC and hippocampus. The magnitude of connectivity predicted self-reported efficacy in a study of smokers

• There was no increased activation or connectivity in ex-smokers with no self-reported craving. This may reflect the cognitive effort to regulate craving in current smokers. RmPFC and mPFC hippocampus connectivity play roles in enhancing cognitive reappraisal.

Transtheoretical Model

A behavior change model that describes the stages individuals go through when modifying behavior, including precontemplation, contemplation, preparation, action, maintenance and relapse. It emphasizes the importance of readiness to change and provides strategies for progression through these stages.

Eagerness scale (SOCRATES)

A tool used to assess an individual's readiness to change substance use behaviors, focusing on factors such as recognition, ambivalence, and taking action towards behavior modification. Low taking steps score associated with increased activation in the Dorsolateral prefrontal cortex

Identifying covert cognition with fMRI

• Spatial navigation and motor imagery tasks can be distinguished

• Motor imagery tasks show activity in the supplementary motor area

• Spatial navigation tasks show activity in the parahippocampal gyrus, posterior parietal lobe and the lateral premotor cortex

Identifying covert cognition with EEG

• A cheaper technique unaffected by implants that can be carried out bedside

• We can see EEG evidence of command following

• It is unlikely that response is simply automatic

• Complex tasks require several aspects of top down cognitive control so suggests conscious awareness

Temporal gap

A period of heightened sensitivity to risk taking

Developmental Neuroscience Informing Public Policy

• The application of findings from developmental neuroscience research to guide legal and social policies, particularly regarding adolescent behavior and brain development.

• Structural development of the brain continues into the 20s and even beyond 30, with the PFC showing particularly late structural development

• Brain systems in basic cognitive processes reach adult levels of maturity by mid-adolescence while brain systems in self-regulation do not fully mature until early adulthood

• Roper vs Simmons is a landmark Supreme Court case that ruled it unconstitutional to impose capital punishment for crimes committed while under the age of 18, highlighting the importance of developmental neuroscience in understanding adolescent cognition and behavior.

Animal Research

• In the Uk, there were 2.9 million procedures involving animals in 2020

• Mice, rats and fish account 92% of this figure but other species were also used

• 1 in 4 people in the UK think animal research should be banned altogether

• 2/3 believe animal research is for medical purposes and there is no alternative

• The BPS code of ethics and conduct covers humans and animals

• There is an obligation to avoid or at least minimise discomfort to living animals

• Any procedure that may cause pain, suffering, distress or lasting harm is regulated under the animals (scientific procedures) act 1986

• This requires a license and is only granted after weighing the benefits of the research against the harms to the animals.

 

Replacement, Reduction and Refinement

Replacement:

• Use existing video materials

• BPS encourages publishing open data to allow secondary analysis

Reduction:

• Required by the animals (scientific procedures) act 1986 to use the minimum number of animals needed for the research goals

Refinement:

• Consider experimental designs that avoid the use of regulated procedures, for example, by enriching rather than impoverishing the environment as the experimental treatment.

Limitations of fMRI for covert cognition

• Physical stress of transporting patient to facility

• Movement effects in imaging data from patients who are unable to remain still

• Metal implants are common in traumatically injured populations and rule out fMRI

Dual Systems Model of Adolescent Risk-Taking

A theoretical framework suggesting that adolescents rely on two distinct cognitive systems: an impulsive system driven by reward sensitivity (socioemotional system), and a reflective system that evaluates risks and consequences (control system). Adolescents have a temporal gap, which is a period of heightened sensitivity to risk-taking

Casey Go/No Task

When emotional information is present, adolescents make more false alarms to positive social cues, and there is enhanced activity seen in the ventral striatum. When no emotional information is present, adolescents perform just as well as adults

Chien et al. Stoplight Task

Adolescents were found to make riskier decisions when peers were present. With this they experience heightened activity in the rewards system. With or without peers, adolescents did not recruit the lateral PFC in the same way adults did.

Broca’s Area

A region in the frontal lobe associated with speech production and language processing.

Positron Emission Tomography

Records metabolic activity in the brain, has poor temporal resolution so cannot tell us exactly when brain activity occurs

Functional Magnetic Resonance Imaging

Measures changes in blood oxygen to see how active the brain is (more active = more oxygen). Has poor temporal resolution so cannot tell us exactly when brain activity occurs

Electroencephalography (EEG)

Measures electrical brain activity via electrodes, has poor spatial resolution (location accuracy) but better temporal resolution

Diffuse Optical Imaging

Shines infrared light into the brain. Light properties change as they pass through oxygenated blood and through active neurons. Has high temporal and spatial resolution

Communication with neurons

1. Dendrites receive input from other neurons via neurotransmitters

2. This causes electrical changes that are interpreted in the cell body (soma)

3. If the signal is strong enough it is passed on as an action potential down the axon

4. Myelin helps to stop the action potential from degrading

5. Axon terminals receive the action potential and release neurotransmitters across the synapse to other dendrites

Membrane potential

The difference in electrical charge between the inside and outside of a neuron. It determines a neuron's readiness to fire an action potential, influenced by ion concentrations across the membrane.

Action potential

The basis for electrical signaling within neurons.

Depolarisation

Caused by dendrites receiving input from other neurons. Repeated depolarisation causes the neuron to reach its threshold membrane potential, which triggers the action potential to travel down the axon

Repolarisation

The process of returning to the resting membrane potential after depolarisation. This occurs as potassium ions exit the neuron, restoring the negative internal charge.

Hyperpolarisation

The process by which the membrane potential becomes more negative than the resting potential, making the neuron less likely to fire an action potential. This is often caused by the influx of chloride ions or the efflux of potassium ions.

Allostatic overload

When physiological responses to stress that promote adaptation in the short term become overused and dysregulated they contribute to pathophysiology, which can have long term effects on the body such as suppressing immune function.

Effects of Chronic Stress: Prospective Memory

Prospective memory is also affected because glucocorticoids bind to the hippocampus which is a critical region for prospective memory. Altered hippocampal functional connectivity in chronic stress predicted prospective memory performance