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I POSTERS / 27TH NORDIC PSYCHIATRIC CONGRESS
Background: Several studies indicate that repetitive transcranial
magnetic stimulation (rTMS) of the left dorsolateral prefrontal
cortex (DLPFC) has a beneficial effect on depressive symptoms.
Aims: To test antidepressant effects of left DLPFC activation by
rTMS.
Method: Ten adults with major depression received two rTMS
treatment periods of 5 days each. During one treatment period the
patients received rTMS over the left DLPFC and in the other treat-
ment period a placebo stimulation. Tlie order of treatment periods
was randomly allocated. Four weeks washout time elapsed between
treatment periods. The patients were evaluated with Flamilton De-
pression Rating Scale (HDRS) before and after each treatment
period by two psychiatrists blind to the nature of the treatment.
Event-Related-Potentials (ERP) using oddball paradigm were re-
corded before and after each treatment period.
Kesults: Changes in depressive symptoms following left DLPFC
stimulalion did not show significant difference compared with
placebo stimulation. There was an increase in P300 amplitude
following left DLPFC stimulation compared with placebo (p =
.044).
Conclusions: Our findings do not support findings that rTMS over
the left DLPFC has antidepressant effects in depressive illness as
evaluated by HDRS.
P - 31 Thursday 14/8, 14:00-15:00
Paired pulse transcranial magnetic stimulation shows
increased cortical inhibition in major depression
Anna L Þórisdóltir1, Ómar Hjaltason2, Ómar ívarsson2, Sigurjón B. StefánssonL
■ Departmcnt of Neurology and ^Department of Psychiatry, Landspitali University
Hospital, Iceland
annaltho@landspitali. is
Background: It is possible to use Transcranial Magnetic Stimulation
(TMS) to probe different cortical inhibitory mechanisms. Pro-
longed cortical silent period (CSP) has been reported in patients
with depressive illness following single pulse stimulation suggesting
increased cortical inhibition.
Ainis: To test cortical inhibition in depression by single and paired
pulse TMS.
Method: Ten patients with major depression and 7 control subjects
were stimulated with a single pulse. All controls and 3 patients had
paired pulse stimulation of equal intensity with 100 ms inter
stimulus interval. Motor evoked potentials (MEP) from voluntary
activated abductor pollicis brevis muscle were recorded. The first
pulse evoked a conditioned MEP and the second pulse evoked a
test MEP.
Results: The duration of CSP was similar in both groups (p = .36).
Mean amplitude of the test MEP was 63 % of the condilioned MEP
for controls but 18 % for the 3 patients tested. The latency of the
test MEP was increased both in controls and patients.
Conclusions: Reduced MEP following the test stimulus suggests an
increased cortical inhibition in depressed patient, but this did not
affect the duration of the CSP.
P - 32 Thursday 14/8,14:00-15:00
Backward visual masking and TMS-induced visual
suppression
H. Magnús Haraldsson. MD, Department of Psychiatry, University of Wisconsin,
Madison, WI 53719. Fabio Ferrarelli MD, Ned H. Kalin MD, Giulio Tononi MD,
PhD.
hm. haraldsson@hosp. wisc. edu
Background: In backward visual masking (BVM), the perception of
a visual stimulus is reduced by a subsequently presented mask. Ab-
normalities in BVM are well established in schizophrenia. Visual
perception can also be suppressed by Transcranial Magnetic Stimu-
lation (TMS) of visual cortex, possibly through similar mechanisms.
Aims: In preparation for a study of TMS-induced visual suppres-
sion in schizophrenics, we examined BVM and TMS-induced sup-
pression in healthy subjects.
Methods: Sixteen subjects were presented with visual stimuli (let-
ters) at one of 4 screen locations. Tlie stimuli were followed, at dif-
ferent inter-stimulus intervals (ISIs), either by a second visual sti-
mulus (mask), or by a single TMS pulses over right occipital cortex.
Results: As expected, B VM was strong at ISIs < 40 milliseconds (ms)
but performance returned to over 90% of normal at ISI = lOOms.
TMS-induced visual suppression was strongest at ISIs between 65
and 95 ms. At those ISIs, error rate was 42-52% for stimuli presen-
ted in the left visual field vs. 10-18% in the right visual field.
Condusions: In normal subjects, right occipital TMS induces left
visual field suppression with a well-defined peak at 65-95ms. Further
studies will investigate whether schizophrenic subjects are abnor-
mally sensitive to TMS-suppression as they are to BVM.
Educational Objectives: At the conclusion of this presentation, the
participant should be able to recognize backward visual masking
and visual cortex transcranial magnetic stimulation (TMS) as tools
for investigating visual processing. We introduce the application of
TMS induced visual suppression for studying populations with
impaired early visual processing, such as schizophrenia patients.
References
I. Amassian VE, Cracco RQ, et al. Transcranial magnetic stimulation in study of
the visual pathway. J Clin Neurophysiol 1998; 15: 288-304.
2. McClure RK. The visual backward masking deficit in schizophrenia. Prog
Neuro-Psychopharmacol & Biol Psychiat 2001; 25: 301-11.
P - 33 Thursday 14/8,14:00-15:00
Mental disorders in a danish working population
Anelia Larsen, Research Fellow, Cand Psych, Unit for Psychiatric Research, Aal-
borg Psychiatric Hospital, Aarhus University Hospital, Mölleparkvej 10, 9000 Aal-
borg, Denmark. Henrik Böggild, Jens T. Mortensen, Povl Munk-Jprgensen.
A PL@psyk. nja. dk
Background: Studies have shown that 20-35% of the working popula-
tion experience stress and approx. 10% minor, usually mixed, anxiety
and depression. Screening for psychiatric morbidity often shows
methodological weakness. Therefore, there is a deficit in knowledge
of prevalence of mental problems in working populations.
Aims: To estimate the prevalence of psychiatric morbidity within
the working population in Denmark.
Mcthod: A cross-sectional mullicentre study utilizing a two-phase
design was carried out in two counties in Denmark in February
68 LÆKNABLAÐIÐ / FYLGIRIT 48 2003/89