Biomedical subjects
A Revonsuo
Publications and source records attributed to A Revonsuo.
Serum estrogen level, attention, memory and other cognitive functions in middle-aged women.
OBJECTIVE: To evaluate the relationship between serum estradiol level and cognitive processing efficiency and memory. METHODS: Sixty-three healthy women aged 45-65 years were recruited through a newspaper announcement. The subjects were divided into two subgroups (low-estrogen group, n = 37 and high-estrogen group, n = 26) according to their serum follicle stimulating hormone (FSH) and estradiol levels. In the high-estrogen group, estrogen was either endogenous or supplied by estrogen replacement therapy. Automatic and controlled cognitive processing and attentional resources were measured using CogniSpeed software, together with conventional tests of cognitive performance: similarities, digit span, digit symbol, block design, object naming and recall, paired word associates (PWA) recall, Benton visual retention and paced auditory serial addition test (PASAT). The Beck depression inventory was also assessed. RESULTS: Cognitive reaction speeds were similar in both groups. Women with low estrogen levels made more errors in the vigilance test (sustained attention, p = 0.040). There were no differences in short-term or long-term memory, or verbal, visual or working memory between the study groups. Older women were slower in the ten-choice reaction time (10-CRT) test (r = 0.25, p = 0.047) and made more errors in the test of suppressing attention (Stroop incongruence test; r = 0.34, p = 0.007) and in the sustaining attention test (vigilance test; r = 0.47, p < 0.001). Depression scores did not correlate with cognitive variables. CONCLUSIONS: Cognitive performance was well preserved in healthy middle-aged women. Cognitive speed, accuracy, attentional resources and memory did not show impairment with decline of serum estrogen level in this age group.
Semantic processing of spoken words in Alzheimer's disease: an electrophysiological study.
Patients suffering from Alzheimer's disease (AD) have severe difficulties in tasks requiring the use of semantic knowledge. The semantic deficits associated with AD have been extensively studied by using behavioral methods. Many of these studies indicate that AD patients have a general deficit in voluntary access to semantic representations but that the structure of the representations themselves might be preserved. However, several studies also provide evidence that to some extent semantic representations in AD may in fact be degraded. Recently, a few studies have utilized event-related brain potentials (ERPs) that are sensitive to semantic factors in order to investigate the electrophysiological correlates of the semantic impairment in AD. Interest has focused on the N400 component, which is known to reflect the on-line semantic processing of linguistic and pictorial stimuli. The results from studies of N400 changes in AD remain somewhat controversial: Some studies report normal or enlarged N400 components in AD, whereas others report diminished ones. One issue not reported in previous studies is whether word-elicited ERPs other than N400 remain normal in AD. In the present study our aim was to find out whether the ERP waveforms N1, P2, N400, and Late Positive Component (LPC) to semantically congruous and incongruous spoken words are abnormal in AD and whether such abnormalities specifically reflect deficiencies in semantic activation in AD. Auditory ERPs from 20 scalp sites to semantically congruous and incongruous final words in spoken sentences were recorded from 17 healthy elderly adults and 9 AD patients. The early ERP waveforms N1 and P2 were relatively normal for the AD patients, but the N400 and LPC effects (amplitude difference between congruous and incongruous conditions) were significantly reduced. We interpret the present results as showing that semantic-conceptual activation and other high-level integration processes are defective in AD. However, a word congruity effect earlier than N400 (phonological mismatch negativity), reflecting lexical selection processes, is at least to some extent preserved in AD.
The neural generation of a unified illusion in human vision.
The neural mechanisms of visual binding in humans were investigated by measuring the brain's high-frequency electric responses (36-44 Hz) to the subjective visual perception of a unified three-dimensional illusion. 40 Hz synchronization was found over occipital and right parieto-temporal areas 500-300 ms before visual awareness of the three-dimensional Gestalt was reported, but not during the viewing of the illusion. At lower frequency bands (8-13 Hz and 13-20 Hz) no corresponding synchronization was found. 40 Hz synchronization thus directly correlates with the construction and emergence of a unified visual percept and may reflect the rapid formation of transient functional connections between spatially separated cortical areas.
Modulation of the parieto-occipital alpha rhythm during object detection.
Changes in the human neuromagnetic alpha rhythm were monitored during an object detection task to study the effects of visual shape processing on the parieto-occipital activity. Pictures of coherent meaningful objects, which the observers had to detect, and of disorganized meaningless non-objects were presented briefly between masks. The non-objects were systematically followed by a higher level of alpha than the objects, the difference emerging on average 400 msec after the stimulus, with a median delay of 130 msec after evoked response onsets in the occipital, temporal, and parietal cortices. Without attention to visual shape, the alpha levels did not differ between objects and non-objects. The alpha level was higher after non-objects than missed objects, and higher after missed than correctly detected objects, suggesting that the alpha level is inversely related to saliency or familiarity of the object and does not directly reflect visual awareness. The reactive alpha rhythm was generated in the parieto-occipital sulcus, which in several primate species includes areas belonging to the dorsal visual pathway. According to current views, the parietal cortex produces attentional signals that filter out irrelevant information in the ventral visual stream. Our results reinforce the idea of bidirectional interaction: information derived from visual shape can rapidly modify activity in the parieto-occipital region. The synchronized alpha oscillations may reflect attenuation of occipito-parietal information transfer and disengagement of parietal cortex from object selection.
Knowledge of concept meanings in Alzheimer's disease.
The present study focuses on semantic deficits in Alzheimer's disease (AD). We distinguish three different levels of semantic knowledge: (1) lexical, (2) semantic-conceptual, (3) conscious understanding. We devised methods that tap levels (2) and (3). Our aim was to determine how much guidance AD patients need to consciously access a given semantic-conceptual field and how well they can understand the meanings of concepts and semantic relations. Four different tasks were used to tap different kinds of concepts, the relationships between concepts and their attributes, and the hierarchical structure among different concepts. The retrieval demands of the tasks were eased by presenting guiding questions. The results revealed that AD patients have deficient voluntary access to semantic-conceptual representations. The deficits persist even in passive recognition and forced-choice tasks. We conclude that AD patients have a generalized access deficit, although some aspects of the results are suggestive of storage deficit.
Visual awareness of objects correlates with activity of right occipital cortex.
In the search for human neural correlates of visual awareness, cortical magnetic responses to coherent and meaningful objects were compared with responses to disorganized and meaningless non-objects when observers tried to detect the coherent objects. Three brief stimulus durations were included to vary the detection rate of the objects. Of the multiple brain regions activated, only the right lateral occipital cortex showed signals correlating with the proportion of correct object detections. The results suggest an important role for this area in visual awareness of objects.
Semantic processing without conscious understanding in a global aphasic: evidence from auditory event-related brain potentials.
We report a global aphasic who showed evidence of implicit semantic processing of spoken words. Auditory event-related brain potentials (ERPs) to semantically congruous and incongruous final words in spoken sentences were recorded. 17 elderly adults served as control subjects. Their ERPs were more negative to incongruous than to congruous final words between 300 and 800 ms after stimulus onset (N400), and more positive between 800 and 1500 ms (Late Positivity). The aphasic showed an exactly similar pattern of ERP components as the controls did, but his performance in a task demanding explicit differentiation between semantically congruous and incongruous sentences was at the chance level. During follow-up, his explicit understanding recovered over the chance level but the ERPs remained fairly similar. We conclude that implicit semantic activation at the conceptual level can take place even in the absence of conscious (explicit) comprehension of the meaningfulness of linguistic stimuli.
Dissimilar age influences on two ERP waveforms (LPC and N400) reflecting semantic context effect.
Age-related changes in semantic context effects were examined using late event-related brain potentials (ERPs). Auditory ERPs to semantically congruous and incongruous final words in spoken sentences were recorded in 16 children (aged 5-11 years) and 16 adults. Previous findings concerning age-related effects on N400 were replicated: the N400 effect was significantly larger in children than in adults. The main new finding was that a late positive component (LPC) following N400 and modulated by semantic context in adults was not found in children. Thus, the common generalization that semantic context effects decline with age holds only for ERP components occurring in the N400 time window or earlier. The cognitive function reflected by the semantic LPC we observed is not clear, but it seems to have a role different from that of the N400, although in adults the components often co-exist as an N400-LPC complex.
Words interact with colors in a globally aphasic patient: evidence from a Stroop-like task.
Stroop-like manual reaction time tasks were administered to 16 controls and one globally aphasic patient who was unable to match written color words with the corresponding color. Although the patient could not explicitly access the meaning of written color words, he showed a similar pattern of performance in the reaction time tasks as the controls: written words were processed automatically and they interacted with the processing of the color of the letters. Thus, the results of this study suggested that it is possible to process unrecognized words implicitly to a cross-domain semantic level where the processing of words interacts with the processing of colors. The results from this and other studies on implicit language processing indicate that linguistic stimuli can be analysed to relatively high levels without any awareness.
Attention related performance in two cognitively different subgroups of patients with multiple sclerosis.
To evaluate the underlying mechanisms of cognitive decline in multiple sclerosis, two clinically and demographically matched multiple sclerosis groups differing in cognitive status were assessed with attention related tasks. In addition to the attention tests recommended by the Cognitive Function Study Group of the American National Multiple Sclerosis Society, a test of sustained attention was used to evaluate the role of possible fatigue on cognitive performance. The cognitively mildly deteriorated group was slower than the cognitively preserved group and the controls on all tests of attention. The mildly deteriorated group did not, however, consistently differ from the other groups in the error scores of the attention tests. The preserved group exhibited slowness at the end of the visual vigilance test, but no deficits were found on the other attention related tests in this group. It is suggested that dissociable kinds of processing slowness are the origin of the deficits found on the attention tests in the two multiple sclerosis groups. Our preserved group exhibited signs of motor and fatigue related slowness, whereas the mildly deteriorated group also had extensive cognitive slowness. As sensitive indicators of cognitive slowness, attentional tests should be included in evaluation of the cognitive status of patients with multiple sclerosis.
Automatic and controlled information processing in multiple sclerosis.
The purpose of this study was to evaluate the kind of slowing of information processing associated with multiple sclerosis and how this possible slowness is related to cognitive deterioration. We selected 45 patients with definitive multiple sclerosis diagnosis and 35 control subjects. Twenty-two patients had mild cognitive deterioration and 23 patients had preserved cognitive capacities, otherwise the groups were matched. Using computerized tests, we investigated three separate stages of information processing: automatic and controlled processing, and motor programming. The results indicate that patients with mild cognitive deterioration are slower than patients with preserved capacities or controls in every stage of processing measured in this study. Additionally, the preserved patients showed signs of mild slowing in automatic visual processing. These results show that, in multiple sclerosis patients, widespread information processing slowness is associated with multiple sclerosis-related cognitive deterioration. This study emphasizes the importance of studying subgroups rather than cognitively heterogeneous patient samples and, furthermore, the need to divide information processing into different stages is indicated.
Slowing of information processing in Parkinson's disease.
In this study, we criticize the notion of bradyphrenia and argue that "slowness of thought" in Parkinson's disease (PD) must be analyzed as slowness of different information-processing stages and that unselected patients should not be used in experimental studies. We selected 32 patients with a long history of PD and 50 control subjects. Sixteen patients had mild cognitive deterioration (not dementia) and 16 patients had preserved cognitive capacities; otherwise the groups were matched. By using computerized tests, we investigated three separate stages: automatic and controlled processing and motor programming. The results indicate that patients with mild cognitive deterioration are slower than patients with preserved cognitive capacities or controls in automatic visual and in controlled processing but not in motor programming. We conclude that the slowing of controlled processing reflects the disruption of central neural networks, that a long history of PD does not necessitate cognitive slowing, and that PD is not a neuropsychologically serviceable category.