The name is absent



432


anomalously high (reflecting low activity) in post-
mortem samples from the left temporal lobe of
schizophrenics (Reynolds 1983).

Friston et al. (1992) also emphasized the frontal
connections in their rCBF analysis. It is in the dor-
solateral prefrontal and cingulate regions that
Petersen and colleagues (Corbetta et al. 1991)
found residual rCBF activation in healthy subjects
after subtracting brain images derived during pas-
sive focussed attention from those obtained under
conditions of divided attention. The cingulate is
also activated during performance of the incom-
patible condition of the Stroop test (Pardo et al.
1990: i.e. read the color of the ink of a word spell-
ing another color). Disorganized schizophrenics
more than others have problems on this part of the
Stroop test and it is this group which shows hypo-
perfusion of the cingulate (Liddle et al. 1992).

In the foregoing paragraphs strikingly mutually
supportive results on limbic function appear from
the comparison of modern imaging techniques
(MRI, PET and ERP), attempts to dissect atten-
tional mechanisms using tasks with specific de-
mands and use of schizophrenic subgroups defined
by symptom cluster rather than diagnosis.

I report briefly an exploratory analysis using this
type of approach. Two subtraction waves, mis-
match negativity (MMN) and difference negativity
(Nd) derived from the passive and active phases
of a З-tone oddball discrimination were compared.
The principle resembles Petersen’s subtraction of
PET-metabolic measures derived under different
stimulus-processing demands. The MMN is the
subtraction ofERPs elicited by common (0.8 KHz)
from rare deviant standard tones (2.0 KHz) under
passive non-attentional conditions. The mismatch
registered represents the difference in pitch and
frequency. The Nd is the result of subtracting ERPs
elicited by a rare 1.4 KHz tone in the passive
condition from the same tone used later as a target
for response.

The MMN is seen as representing a short-term
stimulus-trace-memory (Naataen 1990) reflecting
a largely automatic comparison process (pace Wol-
dorff et al. 1993). It was recently reported to be
markedly reduced in a heterogeneous group of
schizophrenics (Shelley et al. 1991). We confirm
this in Fig. 4 and show that the attenuation is
marked for both paranoid and non-paranoid groups
whether defined by clinical diagnosis or
active
symptoms
scored after the test in a semi-structured
interview. Further we show that there
is a differ-
ence between sub-groups, but only if they are sepa-
rated by
active symptoms. In the paranoid group
MMN is halved but this tends to be more than in
the non-paranoid group where MMN is >75% at-
tenuated at frontal sites. In the context of the em-
phasis above on reports of anomalous temporal
lobe function, it is of interest that particularly those
schizophrenics without paranoid symptoms show
an anomalous negativity at the T6 site (and less so
at T5: Fig. 4).

In contrast to the MMN, Nd is present in both
schizophrenic sub-groups (Oades et al. 1993). But
if the groups are separated by symptoms, Nd is
significantly attenuated over left frontal∕right
parieto-temporal sites in paranoid and over right
frontal/ left posterior parietal sites in the non-para-
noid group (Oades et al. 1994).

This result, obtained with teenaged patients soon
after admission, cannot exclude a potential influ-
ence of medication. The same subjects performed
a conditioned blocking task. This tests the extent
to which they learned about a superfluous stimu-
lus that was nonetheless relevant to task-solution.
While most paranoid patients performed relatively
normally, ignoring the redundant stimulus, non-
paranoids often showed attenuated blocking. How-
ever the non-ρaranoid group also showed increased
DA utilization, as measured in 24 h urine samples

Fig. 4. Top: Bilateral symmetric fronto-parietal distribution of MMN in healthy subjects (200-260 msec: see text) scale +3.0 to
-4.1 uv. Alongside t-test differences are compared to paranoid (P) and non-paranoid (NP) schizophrenics (line shows t(31) 1.7,
p < 0.05).
Left: MMN in schizophrenics diagnosed as paranoid (12) and non-paranoid (16): A) MMN at 6 sites (bin 4 msec), B)
topography 200-260 msec (scale +2.4 to -2.5 uv), c) no significant t-test differences between psychotic groups (200-260 msec).
Right: MMN in schizophrenics with active paranoid symptoms (13) (rated post-test by median split of SANS-SAPS scores)
vs. non-paranoids (15). A) B)
as above, C) t-tests between psychotic groups p < 0.05% at frontal sites (P > NP), T3 and T6
(NP > P).



More intriguing information

1. Target Acquisition in Multiscale Electronic Worlds
2. The name is absent
3. Innovation and business performance - a provisional multi-regional analysis
4. Delayed Manifestation of T ransurethral Syndrome as a Complication of T ransurethral Prostatic Resection
5. Improvements in medical care and technology and reductions in traffic-related fatalities in Great Britain
6. Iconic memory or icon?
7. Wettbewerbs- und Industriepolitik - EU-Integration als Dritter Weg?
8. The Shepherd Sinfonia
9. TECHNOLOGY AND REGIONAL DEVELOPMENT: THE CASE OF PATENTS AND FIRM LOCATION IN THE SPANISH MEDICAL INSTRUMENTS INDUSTRY.
10. Should Local Public Employment Services be Merged with the Local Social Benefit Administrations?
11. The name is absent
12. The name is absent
13. The name is absent
14. CONSIDERATIONS CONCERNING THE ROLE OF ACCOUNTING AS INFORMATIONAL SYSTEM AND ASSISTANCE OF DECISION
15. The name is absent
16. EU enlargement and environmental policy
17. Testing Gribat´s Law Across Regions. Evidence from Spain.
18. Conflict and Uncertainty: A Dynamic Approach
19. The value-added of primary schools: what is it really measuring?
20. Two-Part Tax Controls for Forest Density and Rotation Time