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Commentary on Laws:What are we Trying toExplain?Chris FrithPublished online: 09 Sep 2010.
To cite this article: Chris Frith (1999) Commentary on Laws: Whatare we Trying to Explain?, Cognitive Neuropsychiatry, 4:1, 31-32, DOI:10.1080/135468099396034
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Commentary on Laws: What are we Trying to Explain?
Institute of Neurology, University College London, UK
Keith Laws provides us with a useful review of the many studies of executive
function in schizophrenia. He makes a number of good points. First, not all
patients with schizophrenia perform badly on frontal lobe tests. Second, in those
patients that do perform badly there is usually evidence of a more general
intellectual impairment. Third, poor performance on tests of executive function
does not necessarily mean executive impairments or frontal lobe damage. All
sensible and informed people would agree with these points. Laws is much less
clear about the implications of these conclusions for future studies of executive
function in schizophrenia.
First I would suggest that we should not expect to find a characteristic
neuropsychology associated with schizophrenia. Schizophrenia is a diagnostic
category including patients who show a wide range of signs and symptoms
which fluctuate over time. Although it is still possible that there is a specific
biological marker associated with this disease I do not think that we should
expect to find a specific psychological marker. In contrast, it is reasonable to
expect to find psychological markers for particular signs and symptoms.
Executive dysfunction (and general intellectual impairment) tends to correlate
with severity of negative signs or disorganisation, but not with severity of
hallucinations and delusions (e.g. Johnstone & Frith, 1996) . This relationship
would be more compelling if it could be demonstrated in longitudinal studies; if
the negative signs resolve does the intellectual functioning return to premorbid
From this symptom-based perspective we would not expect to find a general
nonspecific executive problem. Negative signs (poverty of speech, flattening of
affect) are associated with a general failure to initiate action, whereas
disorganisation (incoherent speech, incongruity of affect) is associated with
failure to inhibit inappropriate action. Both these problems could arise from an
impaired executive system, but these signs occur independently of each in cross-
sectional studies of schizophrenia (e.g. Johnstone & Frith, 1996). There is
currently much interest in fractionating the executive system using both lesion
studies and brain imaging. I would expect to see different kinds of executive
problem associated with different aspects of schizophrenia.
The success of attempts to fractionate the executive system will depend to a
considerable extent on our ability to develop more specific models of executive
function. This will, in turn, lead to the development of novel test procedures.
The current standard frontal tests used by neuropsychologists tend to be crude
and underspecified in terms of the cognitive processes which they engage.
Results with laboratory tests suggest that schizophrenic patients are only
impaired on certain executive processes (e.g. Hutton et al., 1998) . A particularly
elegant example, also quoted by Laws, is the study by Elliott, McKenna,
Robbins, & Sahakian (1995) demonstrating that patients with negative features
showed marked response perseveration, but having no difficulty in switching
attention to a previously irrelevant stimulus dimension. Progress in our
understanding of the signs and symptoms of schizophrenia will require studies
of executive processes which are conducted at this level of detail.
REFERENCESElliott, R., McKenna, P.J., Robbins, T.W., & Sahakian, B.J. (1995). Neuropsychological evidence
for frontostriatal dysfunction in schizophrenia. Psychological Medicine, 25, 619630.
Hutton, S.B., Puri, B.K., Duncan, L.-J., Robbins, T.W ., Barnes, T.R.E., & Joyce, E.M. (1998).
Executive function in first episode schizophrenia. Psychological Medicine, 28, 463474.
Johnstone, E.C., & Frith, C.D. (1996). Validation of three dimensions of schizophrenic symptoms in
a large unselected sample of patients. Psychological Medicine, 26, 669679.