Stages of nonsymbolic number processing in occipitoparietal cortex disentangled by fMRI adaptation

The neurobiological mechanisms of nonsymbolic number processing in humans are still unclear. Computational modeling proposed three successive stages: first, the spatial location of objects is stored in an object location map; second, this information is transformed into a numerical summation code; third, this summation code is transformed to a number-selective code. Here, we used fMRI-adaptation to identify these three stages and their relative anatomical location. By presenting the same number of dots on the same locations in the visual field, we adapted neurons of human volunteers. Occasionally, deviants with the same number of dots at different locations or different numbers of dots at the same location were shown. By orthogonal number and location factors in the deviants, we were able to calculate three independent contrasts, each sensitive to one of the stages. We found an occipitoparietal gradient for nonsymbolic number processing: the activation of the object location map was found in the inferior occipital gyrus. The summation coding map exhibited a nonlinear pattern of activation, with first increasing and then decreasing activation, and most activity in the middle occipital gyrus. Finally, the number-selective code became more pronounced in the superior parietal lobe. In summary, we disentangled the three stages of nonsymbolic number processing predicted by computational modeling and demonstrated that they constitute a pathway along the occipitoparietal processing stream

Neurophysiological alterations during phoneme and word processing in the acute stage of aphasia

Only a few studies have investigated neurophysiological substrates of phonological impairment in patients with aphasia (PWA) in the acute stage after stroke (Ilvonen et al., 2003; Nolfe et al., 2006). Behavioral evaluation is often problematic or even impossible in PWA in the acute stage, as some patients cannot be instructed due to severely impaired comprehension, reduced consciousness or confusion. Event-related potentials (ERPS) can circumvent such problems as they have already demonstrated their sensitivity and usefulness in measuring certain language processes in both a healthy and clinical population. The objective of the present study is to investigate neurophysiological substrates of phoneme and word processing in PWA with phonological disorders (PWA-PD) in the acute stage after stroke. Ten PWA-PD (5 men, 5 women; mean age 69.4 years +/- 3.46) are included and compared to 44 healthy control participants (HC) (20 men, 24 women; mean age 44.46 years +/- 13.76). All patients suffer from a first-ever stroke in the left hemisphere, are right-handed, have Dutch as native language and present with acute phonological disorders as established with the Psycholinguistic Assessment of Language Processing in Aphasia (Bastiaanse et al., 1995). PWA-PD admitted with a recurrent stroke, left handedness, indications for comorbid cognitive disorders and severe hearing deficits are excluded. Phoneme discrimination is studied in a pre-attentive (MMN) and attentive (P300) oddball task with respect to the phonemic contrasts place of articulation (PoA), voicing and manner of articulation (MoA) to explore whether a qualitative pattern of impaired phonemic contrast sensitivity can be determined. Word recognition is studied in a pre-attentive oddball task, which consists of differentiating real words from pseudowords. The electroencephalogram (EEG) is recorded through 23 Ag/AgCl-electrodes using a linked ears reference and an electrode placed on the forehead as ground. Further EEG analysis includes additional filtering, independent component analysis, segmentation, baseline correction and artifact rejection. Statistical analysis is performed on amplitudes and latencies specifically taking into account the large heterogeneity among PWA-PD. During phoneme discrimination, PWA-PD only show MMN amplitude reductions with voicing as phonemic contrast in the pre-attentive condition, whereas all three phonemic contrasts reveal smaller P300 amplitudes compared to HC in the attentive condition. PWA-PD show a larger response to PoA compared to MoA and voicing in the pre-attentive condition, whereas in the attentive condition only the difference between PoA and voicing remains. During word recognition, PWA-PD and HC display larger responses to pseudowords compared to real words from 100 ms onwards, continuing in the P200 and N400 time windows, despite the fact that responses to pseudowords show longer latencies in PWA-PD. In summary, this demonstrates a distinct pattern of impaired phonemic contrast sensitivity in PWA-PD, with PoA being the most resistant, voicing the most vulnerable and a substantial effect of attention. Moreover, PWA-PD suffer from a delay in lexical access due to a less efficient information transfer, which did not impair the response to pseudowords. For possible clinical implementation of ERPs, pre-attentive tasks seem to be more suitable than attentive tasks in the acute stage of aphasia

Quantitative analysis of language production in Parkinson's disease using a cued sentence generation task

The present study examined language production skills in Parkinson's disease (PD) patients. A unique cued sentence generation task was created in order to reduce demands on memory and attention. Differences in sentence production abilities according to disease severity and cognitive impairments were assessed. Language samples were obtained from 20 PD patients and 20 healthy control participants matched for age, sex and educational level. In addition, a cognitive test for verbal memory and resistance to cognitive interference was administered. Statistical comparisons revealed significant language changes in an advanced stage of the disease. Advanced PD patients showed a reduction in lexical diversity in notional verbs, which was absent in nouns. Cognitive dysfunctions such as impaired verbal memory are suggested to contribute to the typical noun/verb dissociation in PD patients. In addition, advanced PD patients produced more semantic perseverations, which may be related to set-switching problems. In conclusion, whether language disturbances in PD are the result of non-linguistic cognitive dysfunctions or reflect pure language deficits exacerbated by cognitive impairments, remains a matter of debate. However, the negative impact of cognitive dysfunctions may be important

Distance in Motion: Response Trajectories Reveal the Dynamics of Number Comparison

Cognitive and neuroscientific evidence has challenged the widespread view that perception, cognition and action constitute independent, discrete stages. For example, in continuous response trajectories toward a target response location, evidence suggests that a decision on which target to reach for (i.e., the cognition stage) is not reached before the movement starts (i.e., the action stage). As a result, instead of a straight trajectory to the correct target response, movement trajectories may curve toward competing responses or away from inhibited responses. In the present study, we examined response trajectories during a number comparison task. Participants had to decide whether a target number was smaller or larger than 5. They had to respond by moving to a left or a right response location. Replicating previous results, response trajectories were more curved toward the incorrect response location when distance to 5 was small (e.g., target number 4) than when distance to 5 was large (e.g., target number 1). Importantly, we manipulated the response mapping, which allowed us to demonstrate that this response trajectory effect results from the relative amount of evidence for the available responses across time. In this way, the present study stresses the tight coupling of number representations (i.e., cognition) and response related processes (i.e., action) and shows that these stages are not separable in time

Cognitive and affective theory of mind in healthy aging

Background Previous studies on the effect of healthy aging on Theory of Mind (ToM) have produced mixed results. A possible explanation may be that different ToM components and types of inference have not systematically been considered. This study examined the effect of aging on ToM by assessing both first and second order cognitive and affective components within a single task. Methods We compared performance of young (M= 18.3y) and older adults (M= 61.0y) on the Yoni task. This task allows for a within-subject assessment of both first and second order cognitive and affective ToM. Results We observed that older adults had longer reaction times than young adults across cognitive and affective first order items. For second order items, this age difference was larger for affective than cognitive items. Results showed no indications that these findings could be explained by age differences in speed/accuracy trade-offs. Conclusion Our findings suggest that decision processes underlying ToM are slower in older adults on both first and second order inferences, but that age differences in these processes between cognitive and affective ToM are selective to second order inferences. We propose that the observed age differences may be associated with cortical and mental changes that occur with aging

Clinical use of event-related potentials in diagnostic and therapeutic evaluation of phonological input processes: a one year follow-up case study

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