Attention & Schizophrenia
Schizophrenia is a psychotic disorder characterised by distorted reality and thinking, impaired emotional responses, poor interpersonal-skills, apathy, and indifference to personal hygiene and welfare. ‘Schizophrenia’ translates as ‘split mind’ highlighting the fragmented nature in psychological function (Bleuler, 1911).
Crow (1980) originally distinguished positive from negative symptoms of schizophrenia, as reflected in the DSM-V diagnostic criteria. Positive symptoms are that which are in ‘excess’ to normal functioning e.g. auditory or visual hallucinations, delusions, experiences of control, and disorganised speech. Whilst negative symptoms are that which reflect ‘deficits’ from normality e.g. affective flattening, alogia, and avolition.
The DSM-V requires 2+ symptoms to be present for 1 month. Additionally, one of the symptoms must include experiencing delusions, hallucinations, or disorganised speech that persists for 6 months. It also asks that someone must display social/occupational dysfunction with the exclusion of mood disorders or of other known organic causes (drugs or a brain disorder).
Attentional problems are an enduring characteristic of schizophrenia, causing significant interference to everyday functioning. Attention is the cognitive process concerning sustained concentration on a specific stimulus, enabling us to use information-processing systems with limited capacity to process large amounts of information available to us from the sense organs and memory stores.
We do not have capacity to attend to everything so we use divided or selective attention to prioritise our focus. Selective mechanisms filter incoming stimuli and processes them to extract meaning (Broadbent, 1958, Treisman, 1964). Schizophrenic sufferers are not able to do this, so instead experience an overwhelming chaotic influx containing disconnected thoughts and images that surge into consciousness which they are unable to interpret, i.e. positive and negative symptoms (Frith, 1992).
This idea is supported in how schizophrenia sufferers poorly perform in information processing tasks such as reaction time, visual tracking, short-term memory, size estimation and categorisation (Wang et al., 2005; Amado et al., 2011; Lysaker et al., 2009).
Attention comprises of 3 networks: alerting (maintaining awareness), orienting (information from sensory input), and executive control (resolving conflict) (Fan et al., 2003b; Posner & Petersen, 1990).
Zahn et al. (1963) established that schizophrenia sufferers struggle responding to warning signals, suggesting an alerting network deficit. Wang et al., (2005) using the Attention Network Test (ANT) undermined this, finding no evidence of abnormality in this network. The ANT is a reliable tool as it is very sensitive in detecting attentional deficits in schizophrenia sufferers as it does in other disorders (Fernandez-Duque and Black, in press; Posner et al., 2002; Sobin et al., 2004), therefore providing validity to the results Wang attained.
The anterior cingulate gyrus is thought to be a key component in the attentional systems. Structural and functional irregularities here have been consistently linked to schizophrenia, whilst its relationship to attentional deficits are still unknown (Carter et al., 1997).
Wang et al., (2005) established that the executive attention network in control participants activates the anterior cingulate, however in schizophrenia sufferers this appears abnormal. Carter et al., (1997) demonstrated abnormal-functioning in the dorsal anterior cingulate in schizophrenia sufferers. Benes, (1989) further revealed cellular abnormalities in the anterior cingulate of schizophrenia sufferers using post-mortem studies. Therefore, schizophrenic attention deficit can confidently be linked to reduced control in the executive network, due to abnormal anterior cingulate (Fletcher et al., 1999).
However, this deficit has similarly been identified in those with borderline personality-disorder (Posner, et al., 2002), Alzheimer’s (Fernandez-Durque and Black, in press) and children under 7 years-old (Rueda et al., 2004). Therefore, although these findings are significant, they are not unique to schizophrenia thus cannot be used as a diagnostic.
Amado et al., (2011) demonstrated abnormal alerting and slower reaction times in schizophrenia sufferers, contrary to Wang et al., (2005). Patients benefited more from the alerting signal in a valid orientation when solving an incongruent task of the ANT - suggesting that schizophrenia sufferers have an altered alerting network. However, the alerting and orienting cues interact to enhance attention performance in resolving conflict, suggesting a feasibility for future cognitive remediation strategies. Nevertheless, this study can be criticised as having a small sample, risking a reduced confidence level from an increased margin of error.
Attentional deficit is underpinned by abnormality in neuronal-pathways, connecting the hippocampus with the pre-frontal cortex (Frith, 1992). MRI’s of schizophrenia sufferers thalamus have also revealed abnormalities in attention (Williamson, 2006), meaning that the cerebral cortex could be becoming garbled from receiving unfiltered information from the thalamus (Andreason et al., 1994), manifesting as schizophrenic symptoms. This thalamic abnormality may therefore evidence why stimulus-overload occurs due to a defect of the brains ‘switchboard’.
Additionally, it has been established that the deletion in the COMT gene has been linked with an increased heritable schizophrenia risk as well as deficits in executive attention (Bish et al., 2005; Sobin et al., 2004), further highlighting links between defective attention and schizophrenia.
References
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