Agustín Turrero

Recruitment of Occipital Cortex during Sensory Substitution Training Linked to Subjective Experience of Seeing in People with Blindness

Over three months of intensive training with a tactile stimulation device, 18 blind and 10 blindfolded seeing subjects improved in their ability to identify geometric figures by touch. Seven blind subjects spontaneously reported ‘visual qualia’, the subjective sensation of seeing flashes of light congruent with tactile stimuli. In the latter subjects tactile stimulation evoked activation of occipital cortex on electroencephalography (EEG). None of the blind subjects who failed to experience visual qualia, despite identical tactile stimulation training, showed EEG recruitment of occipital cortex. None of the blindfolded seeing humans reported visual-like sensations during tactile stimulation. These findings support the notion that the conscious experience of seeing is linked to the activation of occipital brain regions in people with blindness. Moreover, the findings indicate that provision of visual information can be achieved through non-visual sensory modalities which may help to minimize the disability of blind individuals, affording them some degree of object recognition and navigation aid.

Dipole density of low-frequency and spike magnetic activity: a reliable procedure in presurgical evaluation of temporal lobe epilepsy.

Conventional visual analysis and dipole density analysis of magnetoencephalographic data for both spike and low-frequency magnetic activity were compared for presurgical evaluation in temporal lobe epilepsy (TLE) in a sample of 26 drug-resistant operated TLE patients. A series of logistic regression analyses were performed. Dipole density sensitivity was superior to visual localization analysis. Three separated logistic models were calculated for interictal spikes, low-frequency magnetic activity, and the combination of both measures. A combined interictal spike/low-frequency magnetic activity model predicted correctly the operated temporal lobe in all patients. Clear-cut criteria for the probability model are proposed that are valid for 92.3% of cases in the sample. The quantitative approach proposed by this study is an evidence-based model for presurgical evaluation of temporal lobe epilepsy, which improves previous magnetoencephalographic investigations and establishes working clinical criteria for patient evaluation in TLE.

Use of the cross-correlation component of the multiscale structural similarity metric (R* metric) for the evaluation of medical images

PURPOSE The aim of the present work is to analyze the potential of the cross-correlation component of the multiscale structural similarity metric (R*) to predict human performance in detail detection tasks closely related with diagnostic x-ray images. To check the effectiveness of R*, the authors have initially applied this metric to a contrast detail detection task. METHODS Threshold contrast visibility using the R* metric was determined for two sets of images of a contrast-detail phantom (CDMAM). Results from R* and human observers were compared as far as the contrast threshold was concerned. A comparison between the R* metric and two algorithms currently used to evaluate CDMAM images was also performed. RESULTS Similar trends for the CDMAM detection task of human observers and R* were found in this study. Threshold contrast visibility values using R* are statistically indistinguishable from those obtained by human observers (F-test statistics: p > 0.05). CONCLUSIONS These results using R* show that it could be used to mimic human observers for certain tasks, such as the determination of contrast detail curves in the presence of uniform random noise backgrounds. The R* metric could also outperform other metrics and algorithms currently used to evaluate CDMAM images and can automate this evaluation task.

Six-Year Training Improves Everyday Memory in Healthy Older People. Randomized Controlled Trial

Purpose of the study: Everyday memory of older persons does not improve with intensive memory training programs. This study proposes a change in these programs based on a time-extended and massive intervention format. Design and Methods: The sample of 1007 healthy older persons (mean age 71.85; SD = 5.12) was randomized into 2 groups. The experimental group followed an extended 6 years of training (192 sessions over 192 weeks) whereas the control group received an intensive training (3 sessions per week for a total of 32 sessions in 11 weeks). The program included cognitive and emotional content whose effects were assessed with the Rivermead Behavioral Memory Test (RBMT) and with the Mini-Mental State Examination (MMSE). Both groups were evaluated initially, after 32 sessions, and again after 6 years. Results: The relative improvements measured with Blom’s derivative showed that everyday memory and mental status of the experimental group were significantly better both in the short (Δ% 8.31 in RBMT and Δ% 1.51 in MMSE) and in the long term (Δ% 12.54 in RBMT and Δ% 2.56 in MMSE). For everyday memory and mental level, the overall gain estimate representing the mean difference in pre-post change between time-extended and intensive groups was 0.27 (95% CI: 0.13–0.40) and 0.54 (95% CI: 0.40–0.67), respectively. Time-extended programs have significantly improved everyday memory in contrast with the usual intensive programs whose effects decay with time. There are also significant increases in mental level scores while daily life functionality is preserved in all subjects who completed the training. Implications: These results suggest that it is possible to preserve everyday memory in the long term with continuous training and practice. Massive and time-extended formats may contribute in the future to a paradigm shift in memory programs for healthy older people.

APOE ε4 Genotype and Cognitive Reserve Effects on the Cognitive Functioning of Healthy Elders

Aim: To test the association between cognitive performance and APOE genotype, and to assess potential modifications of this association by sociodemographic and neuroanatomical factors in a sample of 74 healthy elders. Methods: Firstly, we explored the isolated role of the APOE ɛ4 genotype (i.e., APOE4) in different neuropsychological tests, and then the effects of its interaction with sociodemographic (i.e., age, gender, and educational level) and neuroanatomical (i.e., hippocampal volumes) variables. Subsequently, we performed the same analyses after dividing the sample into two subgroups according to their Mini-Mental State Examination scores (control-high group ≥29 and control-low group < 29). Results: In the whole group, APOE4 carriers exhibited a significantly poorer execution in several cognitive domains including global cognitive functioning, episodic memory, verbal fluency, and naming. This effect was more noticeable in older and less educated subjects. The separated analyses revealed that APOE4 carriers in the control-low group exhibited lower scores in global cognitive functioning and episodic memory, while no effects were observed in the control-high group. Neither gender nor hippocampal volumes showed a significant interaction effect with APOE genotype. Conclusions: Current results point out that APOE4 genotype influences healthy aged cognition, although factors such age or educational attainment seem to modulate its effects.

IC-P-046

Background: Subjects with mild cognitive impairment (MCI) are at higher risk of suffering from Alzheimer’s disease (AD). Previous investigation (Fernández et al, 2002; 2003; 2005) demonstrated that MEG temporoparietal dipole densities of low-frequency activity are good predictors of individuals’ cognitive status, and might be a useful tool to investigate the conversion from MCI to AD. Objective(s): We investigated the role of low-frequency dipole densities as predictors of risk of developing AD. Methods: Whole-head magnetoencephalographic recordings were obtained from 19 probable AD patients, 17 MCI patients, and 17 healthy control subjects. The generators of focal magnetic slow waves were located employing a single moving dipole model. Results: Left parietal delta dipole density (LPD) permitted a reliable classification of AD and MCI patients (sensitivity was 0.737, specificity 0.765, and total classification accuracy was 75.0%), while right occipital dipole density permitted a reliable classification of MCI patients and controls (sensitivity was 0.706, specificity 0.882, and total classification accuracy was 79.4%). Once LPD was confirmed as a reliable variable for the classification of AD and MCI patients a follow-up study was performed. The 17 MCI patients were followed for two years, with a clinical evaluation every 6 months; no loss to follow-up occurred. The cohort was divided into two groups based on a median split of the LPD measure: MCI-High, and MCI-Low. The two groups of MCI patients did not differ in terms of age or MMS score at baseline. After two years 5/17 patients (29.41%) met criteria for Probable AD. MMSE scores were significantly (p 0.042) reduced (8.8 7.01 points) in the converter group from baseline. Four of the 8 (50%) MCIHigh patients developed AD, while only 1 out of 9 (11%) MCI-Low patients converted to dementia (RR 4.5, 95% CI .86 28.3). The estimated relative risk of conversion to AD was increased by 350% in those MCI patients with high LPD scores (MCI-High group). Conclusions: Results confirmed the important role of parietal delta dipole density in the evaluation of AD and MCI. A MEG-based assessment of AD and MCI patients might be considered a useful clinical test in the near future.

Relative efficiency of a censored experiment in terms of Fisher information matrix

Fisher information matrix is used to quantify information loss in the randomly right-censored model, A real value approach alternative to the matrix approach of Turrero (1988) is presented for obtaining real valued measures of the relative efficiency of the censored experiment. Properties of the proposed measures are examined. The connection between both approaches and the Bayesian approach to this problem is also studied. Results in the paper are exemplified by considering grouped survival data.