Mental illness

• What is BOLD signalling ?:

  Consists of local field potential (the sum of field potentials) and multi-signal unit activity.

  BOLD is not a reflection of single and multi-unit neurone activity but instead provided alternate information than neuronal activity and can compliment one another.
• To analyse BOLD data we must consider:

  Spatial processing of the images as ppts brains will all be different , and which voxels to analyse because there thousands and too many can lead to a multiple comparisons problem.
• Underlying assumptions of fMRI include:

  • Cognitive subtraction
  • Extending methodology to patient groups
  • Resting state
• fMRI assumption 1: Cognitive subtraction: 


  Assumes psych process occurring is a real one- we'll never know if the brain is going something in error, also assumes the brain processes are manipulated in isolation and the brain's process for psychological processes are localised.
• fMRI assumption 2: Extending methodology to patient groups:

  Assumes patient groups brain's structures and functions are the same as the control group EXCEPT for the ones being studied. Also assumes all ppts used the same brain processes/ techniques to do the task.

  fMRI doesn't show if structures are abnormal- just abnormal activity.
• fMRI assumption 3: Resting state:

  Assumes resting state is a reflection of mental state when doing nothing - when likely it's a new scenario where the brain will be intaking new sensory information.
• fMRI provides researchers:

  • "Pseudo-insight" to psychological processes.
  • Researchers often fall into consistency fallacy (which assumes that if data is consistent with a theory it is supporting of the theory- which is not always the case).
  • Encourages cherry-picking so researchers can pick studies which best support their theories.
• Fletcher et al (1998) 


  Measured brain activations produced by memory load of schizophrenia patients, found increased activation in left frontal cortex.

  Argued that we cannot determine that the increased activation in left frontal cortex was caused by the task, is a consequence of the task or compensation of the task. We can only say abnormal activation occurs there in task x.
• Powers et al (2017)


  Delusions and hallucinations may be evolving shifts in the balance between top-down experience-dependent expectation and bottom-up sensory evidence. To deal with the noisy sensory information the brain relies on prior experience.
• Cognant and Asby (1970)


  Any system which tries to regulate another (e.g., the brain controlling the world) must remodel the structure and function of the world it inhabits.
• von Helmholtz 


  Perception is an inferential process (Abduction) meaning the perception we experience explains sensory input.
• Bayes: 


  The best abduction is one where sensory input is consistent with that input, but is also the most probable cause. Probability depends on the likelihood that the sensory input is consistent with the cause and the prior is the probability of the cause.
• Hierarchal predictive processing: 


  Considers predictive process as a hierarchically stacked system of broadly similar computations when predictions from higher levels (e.g., abstract concepts or beliefs) act downward and result in prediction errors being fed forward.
• Brain models predict the world, but this is difficult because of:

  Quantity of stimuli, delay and ambiguity.
• If the prediction error is large enough,

  The production must be altered, or small enough that it can be ignored.
• How we understand the world is based on:

  Priors (existing knowledge which is in Bayesian formulations).
• Teufel et al (2018)

  Tested ppts ability to detect ambiguous contours in a two-tone image (making the contour implied). Found that high level semantic knowledge of the images content inhanced ppts ability to detect the contour, both healthy ppts and patients in early psychosis stages were equally bad. Then once prior knowledge was given, ppts in psychosis did significantly better.
• Illusions and psychosis: 


  Illusions e.g., McGurk effect and hollow mask show that we are all capable of perceptions which deviate from reality.
• Sterzer et al (2008) 


  Despite having training on RDk stimuli moving side-to-side, ppts believed that the alternative movement pattern was due to the blue-green glasses not their perceptual experience.
• Balance in the system 


  The system must find a balance between being overly responsive to signals which aren't truly reflexive of reality and signals which truly aren't real.
• Charles Bonnet Syndrome: 


  Characterised by visions which are initially perceived as real, but patients can realise that the visions don't reflect reality.

  Believed to be caused by a decrease in strength to visual inputs.
• Trauma and perception 


  In people with PTSD or who have experienced traumatic experiences- especially at younger ages- have responses which 'tell' them to expect similar treatment from others.

  Unpredictability, uncertainty and hostility exacerbate this, meaning a stimulus believed to be non-salient to another is salient to a traumatised person. Meaning higher order beliefs influence how we interpret sensory inputs by using previous knowledge. System seeks out evidence to support its own predictions.
• Ketamine- how it works and relates to psychosis:

  Ketamine blocks NMDA receptors and enhances dopamine release. This is believed to inhibit prior expectation messages in the hierarchy model causing a disturbance to top-down, bottom-up processing.

  Ketamine has been noted to cause psychosis like states in people and the above reasons are why.
• Predictive processing and schizophrenia:

  Predictive processing theory suggests that low level neurochemical changes e.g., changes in dopamine, via signalling could (theoretically) generate a subjective sense that previous expectations are wrong. Causing the person to seek new expectations- some of which may seem outlandish to outsiders.

  This system imbalance can be made worse due to trauma.

  Could also explain prodrome symptoms (early symptoms of psychosis).
• Sense of agency: 


  We and we alone have caused the actions we are performing.

  Is a causal interference which requires sensory information and previous knowledge.
• Agency is...


  Tricky to measure as it is a subjective experience (you either have to measure it via self-report or by intentional binding (implicit measure)). It's below our awareness and is potentially related to control.
• Spence et al (1997)

  Asked patients with delusions of control to take paced random joysticks movements. Ppts were able to perform this perfectly, but all believed they were not the agents of the movements.

  Therefore knowing the goal state and meeting the goal doesn't seem to be sufficient to generate sense of agency.
• Fourneret et al (1998)


  Ppts couldn't see one hand that was drawing found that ppts were able to counteract computer made deviations but were unaware of the magnitude of their re-adjustment.

  We are equally unaware of how much movement adjustment is required in a given action. Meaning that our reliability and importance of proprioceptive feedback must be questioned.
• Difference between intended and non-intended actions is:

  Intended actions have more predicable consequences.
• Shergill et al (2003): Force cancellation effect: 


  If a person cancels the sensory consequences of their own action, when asked to replicate a force which has been externally applied they will produce too much force in order to feel a force which seem to match the force applied.
• Wolpert et al: Model of movement control:

  Requires that the goal is represented as an intended state, and when compared to the current state an inverse model is created to generate inverse model of motor commands, which creates a forward model. The forward model creates a predicted state which is compared to the intended state which if is incorrect, an error signal is sent to modify the inverse mode.
• Sense of agency requires: 


  External cues including priority, consistency with surroundings and exclusivity (must be the only plausible cause of external consequences).
• Anosognosia for Hemiplehia: 


  Inability to acknowledge that you are paralysed and the belief that the paralysed limb can move. Person can claim a movement has failed but the limb is still functional.

  Believed to be a motor control and agency disorder.
• Alien hand syndrome


  Patient denies that the limb belongs to them and may even belong to someone else.
• Hellman et al (1998): Theory for Anosognosia for Hemiplehia: 1:

  Hypothesised that Anosognosia for Hemiplehia was caused by a failure to form motor intentions and so the forward model doesn't prime comparator to expect a movement and so patients never 'discover' that they can't move the limb.
• Frith et al (2000): Theory of Anosognosia for Hemiplehia: 2: 


  Anosognosia for Hemiplehia patients are able to predict sensory consequences but fail to register the difference between predicted and actual sensory feedback due to sensory feedback deficits.
• Feinberg et al (2000)

  Alien hand syndrome is caused by an attenuation of sensory feedback meaning that patients don't identify the body as their own. We don't know if this is why they believe it belongs to someone else.
• Marchetti et al (1998): Anarchic hand syndrome 


  Person recognises the hand as their own but feel that it is beyond their control.
• Utilisation behaviour: 


  The perception that someone else's movements appear externally driven.
• Possible explications fro anarchic hand syndrome include:

  Patients view certain objects are having the ability to move (motor affordances)