- Email: [email protected]
Temporal-lobe asymmetry in image recognition-1Z
Abstracts /International Journal of Psychophysiology 25 (1997) 17-84
tones when the stimuli were attended to had sources in the visual cortex of the blind subjects, evoked electrical brain activity was localized in one subject of each group with a 122-channel magnetometer. Deviant tones elicited prominent magnetic fields in the visual cortices of both the early-blinded and late-blinded subject but no evident response in the visual cortex of the sighted subject. The present results, indicating visual-cortex activity in subjects blinded early and late in life, suggest that cross-modal plasticity is possible even in the mature human brain. DECREASED AEF PEAK LATENCIES ALCOHOLICS
IN ABSTINENT
J. Ahveninen*‘, E. Pekkonen’~2, T. Kujala’, R. Ntitinen’, K. Sepp$, P. SilIanaukee4 and I.P. Jllskehiinen’ ‘Cognitive Brain Research Unit, Department of Psychology, POB 11, FIN-00014, University of Helsinki, Finland; *BioMag Laboratory, Medical Engineering Center, Helsinki University Central Hospital, Finland; 3Medical School/General Practise, University of Tampere, Finland; 4Alcohol Related Diseases, Pharmacia AB Diagnostics, Upp sala, Sweden Our purpose was to investigate the functional brain deficits in abstinent alcoholics with the 122~channel whole-head magnetometer. Auditory evoked magnetic fields (AEF) were recorded using passive odd-ball paradigm from 13 abstinent alcoholics with no other diseases and 10 healthy age-matched controls. Standard (80%) and deviant (20%) tones were presented monoaurally to each ear, in four separate blocks with constant inter-stimulus intervals (ISI) of 0.5 and 2.5 s. The peak latency of the ipsilateral Nlm-wave was significantly decreased in the alcoholic group when the tones were presented to the right ear and ipsilateral Plm-amplitude of the alcoholics tended to be enhanced during both left-ear and right-ear stimulation. The peak latency of the mismatch field (MMF), elicited by the deviant tones, had a significant group by IS1 interaction: the MMF of the alcoholics peaked significantly earlier compared to the controls when the IS1 was 2.5 s. The results might reflect reduced striato-thalamic gating of sensory input to the auditory cortex due to impaired inhibitory neurons caused by alcohol. TEMPO-LOBE NH-ION-1Z
ASYMMETRY
IN IMAGE RECOG-
S. Vannil*, A. Revonsuo’, J. Saarinen’ ‘Brain Research Unit, Low Temperature University of Technology, 02150 Espoo, ‘Centre for Cognitive Neuroscience, 20520 Turku, Finland
and R. Hari’ Laboratory, Helsinki Finland University of Turku,
Cortical magnetic fields were recorded with a whole-scalp neuromagnetometer to visual stimuli from 8 observers. The
41
stimuli were either ‘images’ (pictures of 200 concrete objects or animals) or ‘non-images’ (generated from the images by randomly rotating circular areas within them), presented once every 3-5 s for 30, 45 and 105 ms in-between backward and forward maskers. The observers indicated their decision about the stimulus type (image vs. non-image) with index finger lift. Most observers (7 out of 8) showed signals in medial occipital cortex, in lateral occipital cortex bilaterally (6) and in superior temporal lobe in or near the midsuperior temporal sulcus (8 left, 6 right) and in the left parietal lobe (6). The temporal lobe responses, peaking at 320-360 ms, were asymmetric for the 105-ms images (with 95% of correct decisions): The left temporal lobe was more active for images than non-images (mean difference 52%, p < 0.005) whereas the right temporal lobe showed opposite tendency, with statistically significant difference between the hemispheres (p < 0.02). Our results imply hemispheric differences in image processing in the ventral visual stream.
DISTINCT CORTICAL ACTIVATIONS TO LUMINANCE AND PATTERN STIMULI-1Z
K. Portin*, S. Salenius, R. Salmelin and R. Hari Brain Research Unit, Low Temperature Laboratory, Helsinki Univ. Technology, 02150 Espoo, Finland
We studied differences in cortical processing of visual luminance and pattern stimuli by recording neuromagnetic signals from 10 healthy subjects with a Neuromag-122rr’r whole-scalp neuromagnetometer. The stimuli were semicircles, 16-17 deg in diameter, either white on a black background (luminance stimuli) or black-and-white 50 X 50 checks on an equiluminant gray background (patterns), shown for 2 s once every 5 s, alternately to the right and left visual hemifield. Both stimuli elicited clear responses over the occipital lobes at 70-170 ms; luminance stimuli evoked additional strong signals over the parieto-occipital region at 180-350 ms. Cortical activation underlying the responses was modelled with a time-varying 3-dipole model, with two dipoles in the occipital visual cortex (one in each hemisphere) and one in the medial parieto-occipital cortex. The occipital activation was contralaterally dominant for both luminance and pattern stimuli, markedly more strongly for patterns. The absolute strength of parietal activation was 40% larger for luminance than pattern stimuli. Relative strengths of the three dipoles (contralateral occipital: ipsilateral occipital: parietal) were 46; 24:lOO for luminance and 100:4:49 for pattern stimuli. These findings suggest that luminance and pattern stimuli activate various visual areas differently. Pattern stimuli activate the occipital lobe with remarkable contralateral dominance, whereas luminance stimuli pre-dominantly activate the parietal lobe in the dorsal visual pathway.
tones when the stimuli were attended to had sources in the visual cortex of the blind subjects, evoked electrical brain activity was localized in one subject of each group with a 122-channel magnetometer. Deviant tones elicited prominent magnetic fields in the visual cortices of both the early-blinded and late-blinded subject but no evident response in the visual cortex of the sighted subject. The present results, indicating visual-cortex activity in subjects blinded early and late in life, suggest that cross-modal plasticity is possible even in the mature human brain. DECREASED AEF PEAK LATENCIES ALCOHOLICS
IN ABSTINENT
J. Ahveninen*‘, E. Pekkonen’~2, T. Kujala’, R. Ntitinen’, K. Sepp$, P. SilIanaukee4 and I.P. Jllskehiinen’ ‘Cognitive Brain Research Unit, Department of Psychology, POB 11, FIN-00014, University of Helsinki, Finland; *BioMag Laboratory, Medical Engineering Center, Helsinki University Central Hospital, Finland; 3Medical School/General Practise, University of Tampere, Finland; 4Alcohol Related Diseases, Pharmacia AB Diagnostics, Upp sala, Sweden Our purpose was to investigate the functional brain deficits in abstinent alcoholics with the 122~channel whole-head magnetometer. Auditory evoked magnetic fields (AEF) were recorded using passive odd-ball paradigm from 13 abstinent alcoholics with no other diseases and 10 healthy age-matched controls. Standard (80%) and deviant (20%) tones were presented monoaurally to each ear, in four separate blocks with constant inter-stimulus intervals (ISI) of 0.5 and 2.5 s. The peak latency of the ipsilateral Nlm-wave was significantly decreased in the alcoholic group when the tones were presented to the right ear and ipsilateral Plm-amplitude of the alcoholics tended to be enhanced during both left-ear and right-ear stimulation. The peak latency of the mismatch field (MMF), elicited by the deviant tones, had a significant group by IS1 interaction: the MMF of the alcoholics peaked significantly earlier compared to the controls when the IS1 was 2.5 s. The results might reflect reduced striato-thalamic gating of sensory input to the auditory cortex due to impaired inhibitory neurons caused by alcohol. TEMPO-LOBE NH-ION-1Z
ASYMMETRY
IN IMAGE RECOG-
S. Vannil*, A. Revonsuo’, J. Saarinen’ ‘Brain Research Unit, Low Temperature University of Technology, 02150 Espoo, ‘Centre for Cognitive Neuroscience, 20520 Turku, Finland
and R. Hari’ Laboratory, Helsinki Finland University of Turku,
Cortical magnetic fields were recorded with a whole-scalp neuromagnetometer to visual stimuli from 8 observers. The
41
stimuli were either ‘images’ (pictures of 200 concrete objects or animals) or ‘non-images’ (generated from the images by randomly rotating circular areas within them), presented once every 3-5 s for 30, 45 and 105 ms in-between backward and forward maskers. The observers indicated their decision about the stimulus type (image vs. non-image) with index finger lift. Most observers (7 out of 8) showed signals in medial occipital cortex, in lateral occipital cortex bilaterally (6) and in superior temporal lobe in or near the midsuperior temporal sulcus (8 left, 6 right) and in the left parietal lobe (6). The temporal lobe responses, peaking at 320-360 ms, were asymmetric for the 105-ms images (with 95% of correct decisions): The left temporal lobe was more active for images than non-images (mean difference 52%, p < 0.005) whereas the right temporal lobe showed opposite tendency, with statistically significant difference between the hemispheres (p < 0.02). Our results imply hemispheric differences in image processing in the ventral visual stream.
DISTINCT CORTICAL ACTIVATIONS TO LUMINANCE AND PATTERN STIMULI-1Z
K. Portin*, S. Salenius, R. Salmelin and R. Hari Brain Research Unit, Low Temperature Laboratory, Helsinki Univ. Technology, 02150 Espoo, Finland
We studied differences in cortical processing of visual luminance and pattern stimuli by recording neuromagnetic signals from 10 healthy subjects with a Neuromag-122rr’r whole-scalp neuromagnetometer. The stimuli were semicircles, 16-17 deg in diameter, either white on a black background (luminance stimuli) or black-and-white 50 X 50 checks on an equiluminant gray background (patterns), shown for 2 s once every 5 s, alternately to the right and left visual hemifield. Both stimuli elicited clear responses over the occipital lobes at 70-170 ms; luminance stimuli evoked additional strong signals over the parieto-occipital region at 180-350 ms. Cortical activation underlying the responses was modelled with a time-varying 3-dipole model, with two dipoles in the occipital visual cortex (one in each hemisphere) and one in the medial parieto-occipital cortex. The occipital activation was contralaterally dominant for both luminance and pattern stimuli, markedly more strongly for patterns. The absolute strength of parietal activation was 40% larger for luminance than pattern stimuli. Relative strengths of the three dipoles (contralateral occipital: ipsilateral occipital: parietal) were 46; 24:lOO for luminance and 100:4:49 for pattern stimuli. These findings suggest that luminance and pattern stimuli activate various visual areas differently. Pattern stimuli activate the occipital lobe with remarkable contralateral dominance, whereas luminance stimuli pre-dominantly activate the parietal lobe in the dorsal visual pathway.