Functional correlates of cognitive performance and working memory in temporal lobe epilepsy: Insights from task-based and resting-state fMRI.

Temporal lobe epilepsy (TLE) is a common form of medically intractable epilepsy. Although seizures originate in mesial temporal structures, there are widespread abnormalities of gray and white matter beyond the temporal lobes that negatively impact functional networks and cognition. Previous studies have focused either on the global impact on functional networks, or on the functional correlates of specific cognitive abilities. Here, we use a two-pronged approach to evaluate the link between whole-brain functional connectivity (FC) anomalies to overall cognitive performance, and how such abnormal connectivity alters the fronto-parietal brain regions involved in working memory (WMem), a cognitive disability often reported by TLE patients. We evaluated 31 TLE patients and 35 healthy subjects through extensive cognitive testing, resting-state functional magnetic resonance imaging (RS-fMRI), and task-based fMRI using Sternberg's task to evaluate WMem. As a group, TLE patients displayed cognitive abnormalities across different domains, although considerable within-group variability was identified. TLE patients showed disruptions of functional networks between and within the default mode network (DMN) and task-positive networks (TPN) resulting in associations with cognitive performance. Furthermore, during the WMem task, TLE patients showed abnormal activity of fronto-parietal regions that were associated with other forms of memory, and alterations of seed-based connectivity analyses. Our results show that different degrees of abnormal functional brain activity and connectivity are related to the severity of disabilities across cognitive spheres. Differential co-activation patterns between patients and healthy subjects suggest potential compensatory mechanisms to preserve adequate cognitive performance.

La Experiencia Fronteriza Modula el Valor Subjetivo de Recompensas Monetarias Demoradas / The Border Experience Modulates the Subjective Value of Delayed Monetary Rewards

Resumen La población en la frontera norte de México experimenta condiciones económicas particulares al interactuar con dos divisas con tasas de inflación diferente por lo que sus patrones de elección intertemporales pueden ser distintos que en población de la misma nacionalidad no expuesta a esta condición. El objetivo es determinar si la experiencia con diferentes tasas de inflación afecta el descuento temporal de recompensas monetarias de dos divisas diferentes a través del contraste entre un grupo de 36 trabajadores de la frontera México-Estados Unidos y 28 trabajadores del centro del País. Cada participante completó dos tareas de descuento temporal, en donde tenían que elegir entre una recompensa pequeña inmediata y otra grande pero demorada. Una tarea involucraba recompensas monetarias en pesos ($8000 para la opción demorada) y la otra en dólares equivalentes de acuerdo a la tasa de cambio. Se encontró que los participantes fronterizos devaluaron más el peso que el dólar en condiciones de demoras grandes y en comparación con su contraparte del interior de la república, quienes descontaron de la misma manera el peso y el dólar. Los resultados son coherentes con la hipótesis del efecto de la inflación sobre la toma de decisiones intertemporales que involucran recompensas monetarias.

Abstract The population on the northern border of Mexico experiences particular economic conditions when interacting with two currencies with different inflation rates, so their intertemporal choice patterns may be different than in the population of the same nationality not exposed to this condition. The objective is to determine if the experience with different inflation rates affects the temporary discount of monetary rewards of two different currencies through the contrast between a group of 36 workers from the Mexico-United States border and 28 workers from the center of the country. Each participant completed two temporary discount tasks, where they had to choose between a small immediate reward and a large but delayed one. One task involved monetary rewards in pesos ($8,000 for the delayed option) and the other in equivalent dollars according to the exchange rate. It was found that border participants devalued the peso more than the dollar in conditions of long delays and compared to their counterparts in the interior of the republic, who discounted the peso and the dollar in the same way. The results are consistent with the hypothesis of the effect of inflation on intertemporal decision making involving monetary rewards.

Visuospatial working memory in toddlers with a history of periventricular Leukomalacia: an EEG narrow-band power analysis.

BACKGROUND: Periventricular Leukomalacia (PVL) affects white matter, but grey matter injuries have also been reported, particularly in the dorsomedial nucleus and the cortex. Both structures have been related to working memory (WM) processes. The aim of this study was to compare behavioral performances and EEG power spectra during a visuospatial working memory task (VSWMT) of toddlers with a history of PVL and healthy toddlers. METHODOLOGY/PRINCIPAL FINDINGS: A prospective, comparative study of WM was conducted in toddlers with a history of PVL and healthy toddlers. The task responses and the EEG narrow-band power spectra during a VSWMT were compared in both groups. The EEG absolute power was analyzed during the following three conditions: baseline, attention and WM retention. The number of correct responses was higher in the healthy group (20.5 ± 5.0) compared to the PVL group (16.1 ± 3.9) (p = 0.04). The healthy group had absolute power EEG increases (p ≤ 0.05) during WM compared to the attention condition in the bilateral frontal and right temporal, parietal and occipital regions in frequencies ranging from 1.17 to 2.34 Hz and in the right temporal, parietal and occipital regions in frequencies ranging from 14.06 to 15.23 Hz. In contrast, the PVL group had absolute power increases (p ≤ 0.05) in the bilateral fronto-parietal, left central and occipital regions in frequencies that ranged from 1.17 to 3.52 Hz and in the bilateral frontal and right temporal regions in frequencies ranging from 9.37 to 19.14 Hz. CONCLUSIONS/SIGNIFICANCE: This study provides evidence that PVL toddlers have visuospatial WM deficits and a very different pattern of absolute power increases compared to a healthy group of toddlers, with greater absolute power in the low frequency range and widespread neuronal networks in the WM retention phase.

Motor potentials by magnetic stimulation in periventricular leukomalacia.

Periventricular leukomalacia is characterized by damage to the brain's white matter and impairments in motor function. Motor-evoked potentials by transcranial magnetic stimulation evaluate corticospinal tract function. We analyzed alterations in motor-evoked potentials in newborns with periventricular leukomalacia. Thirty infants (aged 4.37 +/- 1.1 months mean +/- S.D.) were divided into three groups: 10 healthy, and 10 with focal and 10 with diffuse periventricular leukomalacia. Potentials recorded in the right abductor pollicis brevis of healthy infants indicated a total motor conduction time of 26.3 +/- 2.4 ms, central motor conduction time of 17.0 +/- 2.6 ms, and central motor conduction velocity of 12.3 +/- 2.2 m/s. In the tibialis anterior, total motor conduction time was 27.4 +/- 2.6 ms; central motor conduction time was 16.7 +/- 2.8 ms, and central motor conduction velocity was 25.2 +/- 3.4 m/s. In the focal periventricular leukomalacia and diffuse periventricular leukomalacia groups, an increase in central motor conduction time and a decrease in central motor conduction velocity (P < 0.05) were evident, without differences between the two groups. Motor-evoked potentials in periventricular leukomalacia revealed an increase in central motor conduction time and a decrease in central motor conduction velocity, without differences between diffuse and focal types.