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Neuropsychological tests measuring frontolimbic deficits and abnormalities of cerebral asymmetry have been used extensively in schizophrenia research.

“Frontolimbic” is a broad term and can refer to number of hypothesised circuits. It is used here to refer to learning and executive functions such as the filtering of information and the

learning systems are believed to be served by the frontolimbic circuitry, including specifically the prefrontal lobes (Stuss and Benson, 1986). There are several circuits connecting the prefrontal and limbic cortex and different deficits that would be expected from breakdowns at different points in the circuit (Frith and Done, 1988). Brooks, Hodde-Vargas and Vargas (1998) found metabolic changes associated with adult schizophrenia in the frontal lobes of children with some or all of the symptoms of schizophrenia in a magnetic resonance spectroscopic study, supporting a neurodevelopmental theory for schizophrenia.

Current researchers have described executive dysfunction in schizophrenia, but with mixed results. Several studies have found that individuals with schizophrenia are impaired on some but not all of a number of executive function measures (Braff, Heaton, Kuck, Cullum,

Moranville, Grant and Zisook, 1991; Morrison-Stewart, Williamson, Coming, Kanuchen, Snow and Merskey, 1992). Discrepancies in the precise characterisation of the general

neuropsychological deficits associated with schizophrenia are due to the heterogeneity of chronic patients who vary in illness duration and symptomatology. Here, a collection of studies will be considered, including those examining executive function in adults and children with schizophrenia, individuals with first episode schizophrenia and early onset schizophrenia, and adults with SPD, in an attempt to delineate the specific executive function deficits in this spectrum of disorders.

Adults

Hanes, Andrews, Smith and Pantellis (1996) evaluated the discriminant validity and homogeneity of planning, set shifting and fluency measures of executive dysfunction in patients with schizophrenia, Parkinsons disease and Huntington’s disease. They found that the 3 tasks could successfully discriminate between the patient group and controls and proposed that the 3 tasks are sensitive and relatively homogenous in their recruitment of executive functions (Hanes et al., 1996).

However, Nestor, Shenton, Wible, Hokama, Odennell, Law and McCarley (1998), whilst finding that thought disorder in the participants with schizophrenia correlated strongly with tests of verbal memory, abstraction and executive functions, reported that neither thought disorder scores nor their neuropsychological correlates were associated with frontal or basal ganglia magnetic resonance imaging (MRI) measures.

Pantelis, Barnes, Nelson, Tanner, Weatherley, Owen and Robbins (1997) measured spatial working memory and planning abilities in participants with schizophrenia and compared them with normal participants and patients with neurological disorders (frontal lobe, temporal lobe, and amygdalohippocampal lesions). Planning ability was measured using the CANTAB “Tower of London” and they found that patients with schizophrenia and frontal lobe lesions made fewer solutions and required more moves for completion. Pantelis et al. (1997) suggest that the results are characteristic of an overall deficit of executive functioning and were similar in pattern to patients with frontal lobe lesions.

Research has also shown that participants with schizophrenia also make perseverative errors on speech and writing fluency tasks. Pennington and Ozonoff (1996) suggest two fluency measures, including the Thurstone Word Fluency Test (Milner, 1964) and the Design Fluency test (Jones-Gotman and Milner, 1977). In a study examining the cognitive impairments associated with schizophrenia, Raine, Dennis, Sauer and Kant (1995) found that participants with schizophrenia were impaired on measures of general intelligence, verbal memory, set shifting and word fluency but not on design fluency. Using a number of executive function measures, including a word fluency measure, Jaquet, Lancon, Auquier, Bourgerol and Scoffo (1997) described frontal cognitive impairments in 42 participants with schizophrenia as compared to normal controls. Basso et al. (1999) used a number of measures in their study to examine the cognitive correlates of negative, disorganised and psychotic symptoms of participants with schizophrenia in an attempt to explore the theory that schizophrenia may be a

heterogeneous set of syndromes rather than a disease entity. The researchers employed several executive function tests, including The Trail Making Test (Part A and B), The

Wisconsin Card Sorting Test and the F-A-S test of verbal fluency and found that the severity of negative symptomatology was related to a worsening of performance across all of the

executive function measures and other neuropsychological measures used. The group of participants with disorganised schizophrenia achieved inverse associations with performance on the measures of IQ, but not on the executive function measures, whilst the psychotic group of participants were not associated with neuropsychological impairment. The authors conclude that the findings demonstrate that distinct schizophrenic symptoms have differing patterns of neurobehavioural correlates.

Early onset/first episode

In a study examining the hypothesis that adolescent-onset schizophrenia represents a distinct neurodevelopmental disease, Basso et al. (1997) found that their adolescent-onset

schizophrenia group performed worse than the aduit-onset and control groups on measures of memory and executive function, supporting previous studies which suggest that patients with schizophrenia who have an adolescent symptom onset have a worse clinical course and greater frequency of cerebral anomalies than those with adult-onset (Basso et al.,1997). In an attempt to circumvent the mixed findings of neuropsychological deficits in individuals with chronic schizophrenia, Hutton, Puri, Duncan, Robbins, Bams and Joyce (1998) designed a methodology to include subjects with first episode schizophrenia and a discrete number of tests to elucidate fundamental cognitive deficits. They measured a range of executive abilities, including planning, spatial working memory and attentional set shifting. The results highlighted that first-episode schizophrenic patients could be characterised by a impoverished ability to plan ahead and construct responses, but an intact ability to switch attention and inhibit prepotent responses in comparison to their matched controls. Hutton et al. (1998) argue that

this study shows that schizophrenic patients do have profound executive impairments even at the beginning of their illness. The findings of this study are particularly important for

understanding the cognitive dysfunction in schizophrenia as other researchers suggest that cognitive impairments in schizophrenia may be a result of prolonged anti-psychotic medication. Other studies have reported that patients with long-term schizophrenia have difficulties with the WCST (see Levin et al., 1989; Elliot and Sahakian, 1995) and are more impaired on the CANTAB attentional set shifting task than on planning and spatial working memory tasks (Elliot, McKenna, Robbins and Shahakian, 1995,1997; Pantelis et al., 1997), whereas the participants with schizophrenia in Hutton et al’s (1998) study do not show a difficulty with this executive function. It does suggest the possibility that the nature of executive dysfunction changes over the course of the illness. However, there are limitations to this piece of research, Hutton et al. (1998) did not subgroup the participants into their specific symptom categories, i.e. paranoid symptoms, passivity experiences or negative symptoms. As mentioned above, previous research has shown that symptom groups within the schizophrenia spectrum show different abilities on theory of mind tasks (Frith and Corcoran, 1996; Garety and Freeman, 1999). The question remains whether executive dysfunctions would be the same or different for different subgroups given that different schizophrenia subgroups perform differently on theory of mind tasks. Whilst Basso et al. (1999) have shown this to be true in their recent study for participants with negative, disorganised and psychotic symptoms, further research is needed to replicate and clarify these findings for the different syndromes within the

Schizophrenia Spectrum of Disorders. Also, further research is needed to examine whether there is a recovery of certain executive function abilities in those individuals who recover from an episode of schizophrenia and who have shown executive function deficits during the acute phase.