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has been previously thought.

Schürmann M, Järveläinen J, Avikainen S, Cannon TD, Lönnqvist J, Huttunen M, and Hari R: Manifest disease and motor-cortex reactivity in twins dicordant for schizophrenia. Br J Psychiatry 2007, 191: 178–179.

Schizophrenia is often associated with difficulties in distinguishing between actions of self and of others. This could reflect dysfunction of the mirror neuron system which directly matches observed and executed actions. We studied 11 people with schizophrenia and their co-twins without manifest disease, using stimulus-induced changes in the magnetoencephalographic approximately 20 Hz rhythm as an index of activation in the motor cortex part of the mirror neuron system. During action observation and execution, motor cortex reaction was weaker in those with schizophrenia than in their co-twins, suggesting a disease-related dysfunction of motor cognition.

Seppä M: High-quality two-stage resampling for 3-D volumes in medical imaging. Medical Image Analysis 2007, 11: 346-360.

This paper introduces a simple method of two-stage resampling where Fourier-domain up-sampling is followed by traditional resampling. Practical aspects as well as efficient implementation techniques are considered. A new version of pruned FFT algorithms to calculate the up-sampling stage is also introduced. The suggested two-stage resampling method provides very high-quality results exceeding those of the previous algorithms. It excels with higher dimensional datasets due to its ability to employ small-support kernels. The applied FFT algorithms make the method most efficient with dataset sizes of powers of two. These reasons and the importance of minimal resampling artifacts make the suggested method especially suitable for 3-D volumes in medical imaging. Furthermore, for repeated uses, only the second stage is recalculated allowing an increase in performance for motion correction applications in functional magnetic resonance imaging (fMRI), for example.

Tanskanen T, Näsänen R, Ojanpää H, and Hari R: Face recognition and cortical responses: Effect of display duration. Neuroimage 2007, 35: 1636–1644.

To clarify the relationship between face perception and cortical activation, we manipulated the face recognition performance of 9 subjects by varying the duration (DUR) of stimuli while cortical neuromagnetic responses were recorded. A face image replaced a continuous pixel-noise mask for 17-200 ms, and the subject reported which of the pre-learned faces had been presented. Two cortical responses were clearly stronger to intact than phase-scrambled faces: the temporo-occipital response peaking at 140-200 ms (M170) and a more widely distributed response peaking at 200-500 ms (M300). For the shortest DURs (17-33 ms), face recognition was at chance level and the cortical responses negligible. For DURs of 50-83 ms, the proportion of recognized faces as well as the strength of cortical responses increased steeply. Recognition performance saturated at DURs of around 100 ms, whereas cortical responses continued to increase until the longest DUR of 200 ms. Amplitudes of both M170 and M300 were thus tightly correlated with recognition performance (r=0.98), but comparison of the increment rates as a function of DUR showed the recognition performance to have an even closer similarity to M170 than

Annual Report 2007

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