Neuropsychologia
-
Human adults can typically visually discriminate the faces of unfamiliar individuals accurately, rapidly, and automatically, i.e. even without the explicit intention to do so. Recent studies have used fast periodic visual stimulation (FPVS) coupled with electroencephalography (EEG) to measure this process with objectivity and high sensitivity during simple non-face related tasks (Liu-Shuang et al., 2014). Here we consider to what extent fast individual face discrimination measured in the human brain with this approach is modulated by a direct face-related task. ⋯ However, this attentional boost strongly reduced response specificity by disproportionately recruiting prefrontal and central parietal regions, thereby blurring the occipito-temporal topography typical of specialized high-level face processing. The individual face discrimination response over face-selective occipito-temporal cortex was modulated by the face-sex task starting from 180 ms onset, followed by activations over prefrontal and central parietal region from 200 ms to 450 ms, respectively. Overall, these findings show that even a robust automatic individual face discrimination response can be further enhanced when explicitly searching for face-related information, albeit with a decrease in response specificity.
-
Injury to the primary visual cortex (V1, striate cortex) and the geniculostriate pathway in adults results in cortical blindness, abolishing conscious visual perception. Early studies by Larry Weiskrantz and colleagues demonstrated that some patients with an occipital-lobe injury exhibited a degree of unconscious vision and visually-guided behaviour within the blind field. A more recent focus has been the observed phenomenon whereby early-life injury to V1 often results in the preservation of visual perception in both monkeys and humans. ⋯ To identify the putative visual pathway/s responsible for this ability, MRI tractography of secondary visual pathways connecting MT with the lateral geniculate nucleus (LGN) and the inferior pulvinar (PI) were analysed. Results revealed an increased PI-MT pathway in the left hemisphere, suggesting that this pulvinar relay could be the neural pathway affording the preserved visual capacity following an early-life lesion of V1. These findings corroborate anatomical evidence from monkeys showing an enhanced PI-MT pathway following an early-life lesion of V1, compared to adults.
-
This study investigated the potential differences in changes to cerebellar grey matter volume (GMV) and functional connectivity (FC) and the association between them, which might elucidate cerebellar function in multiple system atrophy (MSA) and idiopathic Parkinson's disease (IPD). ⋯ Cerebellar GMV loss and cerebellar FC alterations showed similarities in IPD and MSA, along with more widespread changes to GMV in motor and cognitive cerebellum and altered DN-DMN FC in MSA. Further research is needed to better describe the alterations of cerebellar GMV in the cognitive cerebellum and association between cerebellar GMV and intracerebellar FC during the early stages of MSA and IPD.
-
Complex cognitive processes, including language, rely on multiple mental operations that are carried out by several large-scale functional networks in the frontal, temporal, and parietal association cortices of the human brain. The central division of cognitive labor is between two fronto-parietal bilateral networks: (a) the multiple demand (MD) network, which supports executive processes, such as working memory and cognitive control, and is engaged by diverse task domains, including language, especially when comprehension gets difficult; and (b) the default mode network (DMN), which supports introspective processes, such as mind wandering, and is active when we are not engaged in processing external stimuli. These two networks are strongly dissociated in both their functional profiles and their patterns of activity fluctuations during naturalistic cognition. ⋯ Thus, using our novel method, we replicate the language/MD network dissociation discovered previously with other approaches, and also show that the language network is robustly dissociated from the DMN, overall suggesting that these three networks contribute to high-level cognition in different ways and, perhaps, support distinct computations. Inter-individual differences in effect sizes therefore do not simply reflect general differences in vascularization or attention, but exhibit sensitivity to the functional architecture of the brain. The strength of activation in each network can thus be probed separately in studies that attempt to link neural variability to behavioral or genetic variability.
-
Deep brain stimulation of the subthalamic nucleus (STN DBS) is known to increase response speed and lower response accuracy in Parkinson's disease (PD) patients. It has been proposed that this speed-accuracy tradeoff is due to enhanced sensitivity of the motor system to sensory information. An alternative possibility is that this effect is due to weakened suppressive processes. The two alternative interpretations can be tested by analyzing the electromyographic activity (EMG) of the response agonists when the patients perform conflict reaction time tasks. In those tasks, fast subthreshold muscle impulses often occur in the agonist of the incorrect response. These impulses are partial errors that are suppressed before being behaviourally committed. ⋯ Contrary to a recent proposal, STN DBS impaired rather than improved action control by weakening erroneous impulse suppression, whether the patients were On or Off their usual medication. These findings are discussed in light of a recent proposal (Servant M, White C, Montagnini A, Burle B, 2015) that reconciles partial errors with accumulation-to-bound models of decision making. Our results suggest that medication specifically lowers the mechanical threshold while STN DBS lowers the mechanical threshold and to a lesser extent the EMG-threshold.