Perceiving and naming actions and objects.

Neuropsychological studies have suggested differences in the cortical representations of verbs and nouns. Assessment of word-class specific deficits often relies on picture naming with different sets of images used for action and object naming. Such a setup may be problematic in neuroimaging studies, as the perception of the image and the actual differences in retrieving verbs or nouns become intertwined. To address this issue, we investigated how different sets of images affect the pattern of activation in action and object naming. In the present fMRI experiment, healthy volunteers silently performed both action and object naming from action images, and object naming from object-only images. A similar network of cortical areas was activated in all three conditions, including bilateral occipitotemporal and parietal regions, and left frontal cortex. With action images, noun retrieval enhanced activation in bilateral parietal and right frontal cortex, areas previously associated with visual search and attention. Increased activation in the left posterior parietal cortex during this condition also suggests that naming an object in the context of action emphasizes motor-based properties of objects. Action images, regardless of whether verbs or nouns were named, evoked stronger activation than object-only images in the posterior middle temporal cortex bilaterally, the left temporo-parietal junction, and the left frontal cortex, a network previously identified in processing of action knowledge. The strong influence of perceptual input on neural activation associated with noun vs. verb naming can in part explain discrepancies in previous lesion and functional neuroimaging studies on the processing of nouns and verbs.

The 3D topography of MEG source localization accuracy: effects of conductor model and noise.

OBJECTIVE: To evaluate the effect that different head conductor models have on the source estimation accuracy of magnetoencephalography (MEG) under realistic conditions. METHODS: Magnetic fields evoked by current dipoles were simulated using a highly refined 3-layer realistically shaped conductor model. Noise from a real MEG measurement was added to the simulated fields. Source parameters (location, strength, orientation) were estimated from the noisy signals using 3 spherically symmetric models and several one- and 3-layer realistically shaped boundary-element models. The effect of different measurement sensors (gradiometers, magnetometers) was also tested. RESULTS: The noise typically present in brain signals masked the errors due to the different conductor models so that in most situations the models gave comparable results. Active cortical areas around the vertex and in the temporal, frontoparietal, and occipital regions were typically found with 2-4 mm accuracy, whereas source localization in several anterior frontal lobe and deep brain structures yielded errors exceeding 2 cm. Localization in anterior frontal regions may benefit most from the use of realistically shaped models. CONCLUSIONS: The traditionally used sphere model is an adequate model for most research purposes. Any means that increase the signal-to-noise ratio are of highest importance in attempting to improve the source estimation accuracy.

Category-specific occipitotemporal activation during face perception in dyslexic individuals: an MEG study.

In dyslexia, it is consistently found that letter strings produce an abnormally weak or no response in the left occipitotemporal cortex. Time-sensitive imaging techniques have located this deficit to the category-specific processing stage at about 150 ms after stimulus presentation. The typically reported behavioral impairments in dyslexia suggest that the lack of occipitotemporal activation is specific to reading. It could, however, also reflect a more general dysfunction in the left inferior occipitotemporal cortex or in the time window of category-specific activation (150 to 200 ms). As early cortical processing of faces follows a sequence practically identical to that for letter strings, both in location and in timing, we investigated these possibilities by comparing face-specific occipitotemporal activations in dyslexic and non-reading-impaired subjects. We found that both the stage of general visual feature analysis at about 100 ms and the earliest face-specific activation at about 150 ms were essentially normal in the dyslexic individuals. The present results emphasize the special nature of the occipitotemporal abnormality to letter strings in dyslexia. However, in behavioral tests dyslexic subjects were slower and more error-prone than non-reading-impaired subjects in judging the similarity of faces and geometrical shapes. This effect may be related to reduced activation of the right parietotemporal cortex at about 250 ms after stimulus onset.

Dynamics of visual feature analysis and object-level processing in face versus letter-string perception.

Neurones in the human inferior occipitotemporal cortex respond to specific categories of images, such as numbers, letters and faces, within 150-200 ms. Here we identify the locus in time when stimulus-specific analysis emerges by comparing the dynamics of face and letter-string perception in the same 10 individuals. An ideal paradigm was provided by our previous study on letter-strings, in which noise-masking of stimuli revealed putative visual feature processing at 100 ms around the occipital midline followed by letter-string-specific activation at 150 ms in the left inferior occipitotemporal cortex. In the present study, noise-masking of cartoon-like faces revealed that the response at 100 ms increased linearly with the visual complexity of the images, a result that was similar for faces and letter-strings. By 150 ms, faces and letter-strings had entered their own stimulus-specific processing routes in the inferior occipitotemporal cortex, with identical timing and large spatial overlap. However, letter-string analysis lateralized to the left hemisphere, whereas face processing occurred more bilaterally or with right-hemisphere preponderance. The inferior occipitotemporal activations at approximately 150 ms, which take place after the visual feature analysis at approximately 100 ms, are likely to represent a general object-level analysis stage that acts as a rapid gateway to higher cognitive processing.

Microbial etiology of community-acquired pneumonia in the adult population of 4 municipalities in eastern Finland.

To determine the etiology of community-acquired pneumonia in the adult population of a defined area, specific antibody responses in paired serum samples, levels of circulating pneumococcal immune complexes in serum samples, and pneumococcal antigen in urine were measured. Samples (304 paired serum samples and 300 acute urine samples) were obtained from 345 patients > or =15 years old with community-acquired, radiologically confirmed pneumonia, which comprised all cases in the population of 4 municipalities in eastern Finland during 1 year. Specific infecting organisms were identified in 183 patients (including 49 with mixed infection), as follows: Streptococcus pneumoniae, 125 patients; Haemophilus influenzae, 12; Moraxella catarrhalis, 8; chlamydiae, 37 (of which, Chlamydia pneumoniae, 30); Mycoplasma pneumoniae, 30; and virus species, 27. The proportion of patients with pneumococcal infections increased and of those with Mycoplasma infections decreased with age, but for each age group, the etiologic profile was similar among inpatients and among outpatients. S. pneumoniae was the most important etiologic agent. The annual incidence of pneumococcal pneumonia per 1000 inhabitants aged > or =60 years was 8.0.

Dynamics of letter string perception in the human occipitotemporal cortex.

The inferior occipitotemporal brain areas, especially in the left hemisphere, have been shown to be involved in the processing of written words and letter strings. This processing probably occurs within 200 ms after presentation of the letter string. It has also been suggested that this activation may differ between fluent and dyslexic readers. Using whole-head magnetoencephalography, we studied the spatiotemporal dynamics of brain processes evoked by visually presented letter strings in 12 healthy adult subjects. Our achromatic stimuli consisted of rectangular patches in which single letters, two-letter syllables, four-letter words, or symbol strings of equal length were embedded and to which variable noise was added. This manipulation dissociated three different response patterns. The first of these patterns took place approximately 100 ms after stimulus onset, originated in areas surrounding the V1 cortex and was distributed along the ventral visual stream, extending laterally as far as V4v. This response was systematically modulated by noise but was insensitive to the stimulus content, suggesting involvement in early visual analysis. The second pattern took place approximately 150 ms after stimulus onset and was concentrated in the inferior occipitotemporal region with left-hemisphere dominance. This activation showed a preference for letter strings, and its strength and timing correlated with the speed at which the subjects were able to read words aloud. The third pattern also occurred in the time window approximately 150 ms after stimulus onset, but originated mainly in the right occipital area. Like the second pattern, it was modulated by string length, but showed no preference for letters compared with symbols. The present data strongly support the special role of the left inferior occipitotemporal cortex in visual word processing within 200 ms after stimulus onset.

Dissociation of normal feature analysis and deficient processing of letter-strings in dyslexic adults.

Neuroimaging studies have revealed that the functional organization of reading differs between developmentally dyslexic and non-impaired individuals. However, it is not clear how early in the reading process the differences between fluent and dyslexic readers start to emerge. We studied cortical activity of ten dyslexic adults using magnetoencephalography (MEG), as they silently read words or viewed symbol-strings which were clearly visible or degraded with Gaussian noise. This method has previously been used to dissociate between analysis of local features and pre-lexical word processing in fluent adult readers. Signals peaking around 100 ms after stimulus onset and originating in the postero-medial extrastriate cortex were associated with increasing local luminance contrast in the noise patches. These early visual responses were similar in dyslexic and non-impaired readers. In contrast, the letter-string-specific responses peaking around 150 ms predominantly in the left inferior occipito-temporal cortex in fluent readers were undetectable in dyslexic readers. Thus, while the early visual processing seems intact in dyslexic adults, the pattern of cortical activation starts to differ from that of fluent readers at the point where letter-string-specific signals first emerge during reading.

Etiology of childhood pneumonia: serologic results of a prospective, population-based study.

BACKGROUND: To investigate the etiology of pediatric community-acquired pneumonia, we conducted a prospective, population-based study covering the total population <15 years of age (n = 8851) in 4 municipalities in eastern Finland. MATERIALS AND METHODS: The number of patients was 201; chest radiographs were available for all cases and paired sera for serologic assays were available for >90% of cases. The methods included assays for antibody response to 3 pneumococcal antigens, specific pneumococcal immune complex assays and conventional antibody tests for mycoplasmal, chlamydial and viral infections. RESULTS: Serologic evidence of specific microbial etiology was obtained in 133 (66%) of the pneumonia patients. Bacterial infection was diagnosed in 102 cases (51%) and viral infection in 51 cases (25%). Streptococcus pneumoniae was the most common agent (57 cases; 28%), followed by Mycoplasma pneumoniae (44; 22%), respiratory syncytial virus (43; 21%) and Chlamydia spp. (29; 14%). Haemophilus influenzae was identified in only 6% and Moraxella catarrhalis in only 3% of the children. More than one specific infection was found in 51 patients (25%). The proportion of pneumococcal cases varied from 24 to 36% by age. Mycoplasma infections were seen mostly in patients > or =5 years and Chlamydia infections in patients > or =10 years of age. CONCLUSIONS: The results of our prospective, strictly population-based study confirm the importance of S. pneumoniae in the etiology of community-acquired pneumonia in children of all ages. M. pneumoniae and Chlamydia pneumoniae are important from the age of 5 years onwards.

Time-varying activation of different cytoarchitectonic areas of the human SI cortex after tibial nerve stimulation.

We followed cortical activation in eight healthy adults after electric stimulation of the left tibial nerve at the ankle. The recordings were made noninvasively with a whole-scalp neuromagnetometer. The first cortical activation peaked in different subjects at 37-45 ms in the foot area of the right (contralateral) primary somato-sensory (SI) cortex, with mean source current orientation perpendicular to the longitudinal fissure. The current orientation changed within the next 5 ms counterclockwise in all subjects, with a mean rotation of 64 degrees. A two-dipole time-varying model, with two dipoles differing by 28-119 degrees in orientation but less than 1 cm in location in the right SI cortex, explained the signal pattern satisfactorily during the first 100 ms. We suggest that the observed field patterns reflect sequential activation of different cytoarchitectonic areas in the foot SI cortex and imply considerable differences in the structural organization between the foot and the hand SI cortices. The initial activation is considered to take place in area 3b facing the interhemispheric fissure, and the later source, due to the systematic rotations of the field patterns, is assumed to reflect activation of area 5 in the anterior wall of the marginal ramus of the cingulate sulcus.