Recognising the self Flashcards
What are the positive symptoms of psychosis presented in the ICD-10?
- Delusions
- Auditory hallucinations
- Abnormalities of behaviour
- catatonia
- overexcitement
- retardation
What are auditory hallucinations observed in psychosis?
‘perceptions in the absence of external stimuli’
- usually derogatory (unpleasant) voices
What is the prevalence of auditory hallucinations in patients with schizophrenia?
60-70%
What is the prevalence of patients with schizophrenia that had made a suicide attempt in response to the voices they heard (Shergill, Murray and McGuire, 1998)?
25%
What are the two hypotheses (models) on the emergence of auditory hallucinations in schizophrenia?
- Like epilepsy, spontaneous firing of the brain over auditory cortex
- > hearing voices - In schizophrenia the awareness of our own thinking (often in words) is lost
- > thoughts that are experienced in one’s head without them tagged as one’s own
- > brain interprets them as external voice
What does the photic stimulation in an fMRI consist of?
- Statistical programme looking at brain activity over time
-> Which parts of the brain were more active during period when flashing the light
compared to period when there was darkness
- increased brain activation = primary visual cortex
What is the problem with fMRI machines when studying auditory hallucinations?
- High level of background noise -> confounding factor
- > different approach required to eliminate the background noise
What is the approach used with an MRI machine to study auditory hallucinations in the brain?
- Scanner off -> no noise
- Scanner on -> noise (2-3 secs): used as cue AND point in time where brain image is captured
- Rest (20-30 secs) at random: used to capture patient’s experience when lying in silence
- repeat multiple time (up to 60 or 100 times)
- Pick out times when hallucinations vs no hallucinations
- There’s a delay in the brain when looking at imaging signals
What do MRI scan results show about patients with auditory hallucinations (Shergill, Brammer, Williams, Murray and McGuire, 2000)?
Activation of auditory cortex AND inferior frontal gyrus (Broca’s area: speech and speaking) when patients are hearing voices
-> both speech generation AND speech hearing areas are active when patients are hearing voices
What is observed in MRI scan results of healthy controls when asked to generate some words (Shergill et al., 2001)?
Activation of inferior frontal gyrus, right homologous area AND auditory cortex
-> similar patterns of activation to patients suffering from auditory hallucinations
What is observed in MRI scan results when healthy controls are compared to patients prone to auditory hallucinations (whilst thinking in words) (Shergill et al., 2003)?
Less activation in people with schizophrenia compared to healthy controls
- in parahippocampal gyrus (responding to novel or unexpected words)
- in cerebellum (motor movements)
- in superior temporal gyrus (auditory processing and speech monitoring)
What do MRI scan results show on listening to external speech between healthy controls and patients prone to auditory hallucinations (Shergill et al., 2010)?
Hearing part of the brain is activated in similar way in patients and controls when listening to someone talking
What do MRI scan results show on the thinking in words between healthy controls and patients prone to auditory hallucinations (Shergill et al., 2010)?
Hearing part of the brain is switched off when thinking in words
- weaker in patients with schizophrenia
What does the study of Shergill and colleagues (2010) on the differences between patients with schizophrenia and healthy controls when listening to external speech and thinking in words?
Model for monitoring your own thinking doesn’t seem to be functioning as efficiently in patients with schizophrenia prone to auditory hallucinations
How is structural connectivity studied?
- Diffusion tensor technology
- White matter fibres that connect different parts of the brain
- Wherever two parts of brain are working together and regularly -> increase in white matter connections
- > examine white matter connections (structural differences)
What is observed on structural connectivity and auditory hallucinations (Shergill et al., 2007)?
- Higher integrity of white matter bundles in superior longitudinal fasiculus = presence of hallucinatory activity and increased or changes in rewiring
- People currently hallucinating tend to have higher integrity,
compared to people not currently hallucinating but were hearing voices in the past,
compared to people who have diagnosis of schizophrenia but have never experienced hallucinations
How can we distinguish the perceptual consequences of our own actions from perceptions caused by others?
Predictive (Forward) models
- motor signals that cause actions can also predict the consequences of the action
- prediction o the sensory consequences of the action, through to appropriate sensory cortex
What is the role of the corollary discharge system?
Attenuates the sensory cortex (brain compensates for prediction of sensory consequences of action)
How can we measure the physiological predictive (forward) model and the corollary discharge system?
Measure the amount of force you need to apply yourself in order to match an external stimulus
What are the observed differences between patients with schizophrenia and healthy people regarding the corollary discharge system (physiological predictive/forward model)?
- Healthy people attenuate their somatosensory cortex when they plan a self-generated movement
- Patients with schizophrenia are significantly more accurate than healthy controls: their corollary discharge system that sends signal from motor to sensory cortex doesn’t work as efficiently
= failure of attenuation resulting in cortical activation (as if it were an actual stimulus)
-> they feel/hear something despite it’s their own action preparation/planning - That failure of attenuation in people with psychosis correlates with their level of symptomatology (frequency of hallucinations)
What are the clinical implications of the findings in neuroimaging on patients with schizophrenia suffering of auditory hallucinations?
- Listen to the patients: their inner speech
- Collaborate with psychologists to alter the observed mechanisms
- Patient strategies competing with language generation and perception
Which patient strategy may attenuate the inner voices experienced?
Talking to someone or listening to something interesting
-> using speech generation/perception cortical areas
What are the novel modulatory approaches that serve to increase or decrease cortical activity in a relatively non-invasive way?
- Transcranial Magnetic Stimulation (rTMS)
- Transcranial direct-current stimulation (tDCS)
How does transcranial magnetic stimulation (TMS) function?
- Alternating magnetic field in coil induces weak electric current in underlying cortex
- At 1Hz (slow TMS), decreases excitation in underlying cortex
- Fast TMS will increase excitation
- Can also inhibit connected regions via propagated trans-synaptic effects
- Some results analogous to long-term depression, with effects lasting weeks
What are the compensatory effects of transcranial magnetic stimulation (TMS) on auditory processing (Tracy et al., 2010, 2014)?
Strong connection between left and right temper-parietal junctions running through corpus callosum
- Low frequency TMS reduces brain activation in underlying brain regions
- Hemisphere that has reduced activity, regardless of what processing, is named over to other hemisphere
What is observed after transcranial magnetic stimulation (TMS) (Gromann et al., 2012)?
Right-sided frontal and temporal areas show high functional connectivity
How does transcortical direct cortical stimulation (tDCS) function?
Running small electrical current though 2 different parts of the brain
What is observed in patients with auditory hallucinations when reducing the activation over the auditory cortex using tDCS (Human et al., 2011)?
After tDCS:
- fast significant drop in activity of hearing and speech related areas
- decrease of hallucination scores
What is the effect of the treatment of refractory auditory hallucinations using real-time fMRI neurofeedback (Fovet et al., 2016)?
Over successive trials and sessions, patients with hallucinations are able to reduce the activation of specific area
