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case where the HVA∕MHPG ratio correlated negatively with CB in the NP group. Here, in
the absence of HV A/D A changes, basal MHPG∕NA was nearly double that in the controls
(Oades et al., 1994). Evidence for a significant role for NA metabolism in psychosis and an
association with negative symptoms has been discussed at length elsewhere (e.g. Homy-
kiewicz, 1982; van Kammen et al., 1990; Yamamoto et al., 1994).
CB in the PH group was unrelated to any biochemical measure. There was evidence that
this group was responding to neuroleptic medication and, in line with this, CB tended to
normalize after the first trial-pair. This is consistent with a recent report that patients with
positive symptoms show an early improvement after the onset of medication on measures
of complex attention and tasks such as the Stroop test where there is a need to switch
mental set (Nopoulos et al., 1994).
Together the results are consistent with our preliminary report that higher DA activity
was found in subjects showing normal CB (Oades et al., 1992). However, they show that it
would be more precise to say that, within limits, relative increases of DA utilization are
associated with increasing CB and not that CB is predicted by high DA turnover, per se.
The results are also consistent with animal studies showing that acute neuroleptic treatment
facilitates latent inhibition (Feldon & Weiner, 1991).
A plausible interpretation of these data refers to a putative function of DA activity in
switching and NA activity in tuning (Oades, 1985). Basically this suggests that DA activity
promotes the likelihood that there will be a change from the input to a given brain area
that predominantly controls the output of this area. Increased NA activity is involved in
tuning between the inputs competing in a given brain area to influence the output. Low DA
activity (less switching) and high NA activity (overtuning) could lead to an inflexibility of
response. This leads to persistence of the ongoing set or strategy and may be illustrated by
the CB performance of NP patients. In contrast PH patients are more able to switch set-
like controls (cf. Nopoulos et al., 1994, above). Perhaps the benefit of increased DA activity
in controls is seen in the proposal of Lubow & Gewirtz (1995) whereby the ability to switch
between controlled and automatic processing of inconsequential events is promoted.
Could the subgroup differences reported here reflect more frontal dysfunction in the NP
group? Siever (1994) noted that the incidence of deficit symptoms in schizotypal patients
correlated with decreased peripheral measures of HVA that in turn correlated negatively
with the performance of tests said to reflect frontal function. The hippocampus and associ-
ated limbic areas are involved in mediating learned inattention in rats (see Introduction);
however, there is a body of evidence suggesting that a number of attention-related effects
in primates are taken over by the frontal lobe (e.g. Oades, 1982, pp. 123-128). Indeed,
recently normal latent inhibition performance was reported in patients with temporal lobe
epilepsy, implying that mesial temporal lobe structures may not mediate learned inattention
in man (Gray et al., 1995). Hence as Siever (1994) reported enlarged ventricles and altered
PET measures of frontal metabolism in neuropsychologically impaired schizotypal patients,
it would be instructive to study neuropsychological performance and tomographic measures
of atrophy and metabolism in patients with a known CB impairment.
Acknowledgements—We should like to thank B. Roepcke and E. Kulisch for assistance with symptom ratings; Dr
H. Bussemass and his assistants at the Dr Eberhard Laboratory, Dortmund, for the monoamine analysis; and J.