Cerebral White Matter Mediation of Age-Related Differences in Picture Naming Across Adulthood

As people age, one of the most common complaints is difficulty with word retrieval. A wealth of behavioral research confirms such age-related language production deficits, yet the structural neural differences that relate to age-related language production deficits remains an open area of exploration. Therefore, the present study used a large sample of healthy adults across adulthood to investigate how age-related white matter differences in three key left-hemisphere language tracts may contribute to age-related differences in language ability. Specifically, we used diffusion tensor imaging (DTI) to measure fractional anisotropy (FA) and radial diffusivity (RD) which are indicators of white matter structure. We then used a series of path models to test whether white matter from the superior longitudinal fasciculus (SLF), the inferior longitudinal fasciculus (ILF), and the frontal aslant tract (FAT) mediated age-related differences in one form of language production, picture naming. We found that FA, as well as RD from the SLF and FAT mediated the relation between age and picture naming performance, whereas a control tract (corticospinal; CST) was not a mediator. Moreover, differences between mediation of picture naming and a control naming condition suggest that left SLF has a greater role in higher-order aspects of naming, such as semantic and lexical selection whereas left FAT is more sensitive to sensorimotor aspects of fluency or speech motor planning. These results suggest that dorsal white matter contributes to age-related differences in generating speech and may be particularly important in supporting word retrieval across adulthood.

Motor planning brings human primary somatosensory cortex into action-specific preparatory states

Motor planning plays a critical role in producing fast and accurate movement. Yet, the neural processes that occur in human primary motor and somatosensory cortex during planning, and how they relate to those during movement execution, remain poorly understood. Here we used 7T functional magnetic resonance imaging (fMRI) and a delayed movement paradigm to study single finger movement planning and execution. The inclusion of no-go trials and variable delays allowed us to separate what are typically overlapping planning and execution brain responses. Although our univariate results show widespread deactivation during finger planning, multivariate pattern analysis revealed finger-specific activity patterns in contralateral primary somatosensory cortex (S1), which predicted the planned finger action. Surprisingly, these activity patterns were as informative as those found in contralateral primary motor cortex (M1). Control analyses ruled out the possibility that the detected information was an artifact of subthreshold movements during the preparatory delay. Furthermore, we observed that finger-specific activity patterns during planning were highly correlated to those during execution. These findings reveal that motor planning activates the specific S1 and M1 circuits that are engaged during the execution of a finger press, while activity in both regions is overall suppressed. We propose that preparatory states in S1 may improve movement control through changes in sensory processing or via direct influence of spinal motor neurons.

Visual, delay and oculomotor timing and tuning in macaque dorsal pulvinar during instructed and free choice memory saccades

Causal perturbation studies suggest that the primate dorsal pulvinar (dPul) plays a crucial role in target selection and saccade planning, but many of its basic visuomotor neuronal properties are unclear. While some functional aspects of dPul and interconnected frontoparietal areas - such as ipsilesional choice bias after inactivation - are similar, it is not known if dPul neurons share oculomotor response properties of cortical circuitry. In particular, the delay period and choice-related activity have not been explored. Here we investigated visuomotor timing and tuning in macaque dPul during instructed and free choice memory saccades using electrophysiological recordings. Most units (80%) showed significant visual (16%), visuomotor (29%) or motor-related (35%) responses. Visual cue responses were mainly contralaterally-tuned; motor responses showed weak contralateral bias. Saccade-related responses (enhancement and suppression) were more common (64%) than cue-driven responses (45%). Pre-saccadic enhancement was less frequent (9-15% depending on the definition), and only few units exhibited classical visuomotor patterns such as a combination of cue and continuous delay period activity up to the saccade onset, or pre-saccadic ramping. Instead, activity was often suppressed during movement planning (30%) and execution phases (19%). Interestingly, most spatially-selective neurons did not encode the upcoming decision during the delay in free choice trials. Thus, in absence of a visible goal, the dorsal pulvinar has only a limited role in the prospective motor planning, with response patterns partially complementary to its frontoparietal cortical partners. Conversely, prevalent cue and post-saccadic responses imply that the dorsal pulvinar participates in integrating spatial goals with processing across saccades.

From Action to Cognition: Neural Reuse, Network Theory and the Emergence of Higher Cognitive Functions

The aim of this article is to discuss the logic and assumptions behind the concept of neural reuse, to explore its biological advantages and to discuss the implications for the cognition of a brain that reuses existing circuits and resources. We first address the requirements that must be fulfilled for neural reuse to be a biologically plausible mechanism. Neural reuse theories generally take a developmental approach and model the brain as a dynamic system composed of highly flexible neural networks. They often argue against domain-specificity and for a distributed, embodied representation of knowledge, which sets them apart from modular theories of mental processes. We provide an example of reuse by proposing how a phylogenetically more modern mental capacity (mental rotation) may appear through the reuse and recombination of existing resources from an older capacity (motor planning). We conclude by putting arguments into context regarding functional modularity, embodied representation, and the current ontology of mental processes.

Kinematic Changes in the Uninjured Limb After a Traumatic Brachial Plexus Injury

Background: Traumatic brachial plexus injury (TBPI) typically causes sensory, motor and autonomic deficits of the affected upper limb. Recent studies have suggested that a unilateral TBPI can also affect the cortical representations associated to the uninjured limb.Objective: To investigate the kinematic features of the uninjured upper limb in participants with TBPI.Methods: Eleven participants with unilateral TBPI and twelve healthy controls matched in gender, age and anthropometric characteristics were recruited. Kinematic parameters collected from the index finger marker were measured while participants performed a free-endpoint whole-body reaching task and a cup-to-mouth task with the uninjured upper limb in a standing position.Results: For the whole-body reaching task, lower time to peak velocity (p = 0.01), lower peak of velocity (p = 0.003), greater movement duration (p = 0.04) and shorter trajectory length (p = 0.01) were observed in the TBPI group compared to the control group. For the cup-to-mouth task, only a lower time to peak velocity was found for the TBPI group compared to the control group (p = 0.02). Interestingly, no differences between groups were observed for the finger endpoint height parameter in either of the tasks. Taken together, these results suggest that TBPI leads to a higher cost for motor planning when it comes to movements of the uninjured limb as compared to healthy participants. This cost is even higher in a task with a greater postural balance challenge.Conclusion: This study expands the current knowledge on bilateral sensorimotor alterations after unilateral TBPI and should guide rehabilitation after a peripheral injury.

Hybrid dedicated and distributed coding in PMd/M1 provides separation and interaction of bilateral arm signals

Pronounced activity is observed in both hemispheres of the motor cortex during preparation and execution of unimanual movements. The organizational principles of bi-hemispheric signals and the functions they serve throughout motor planning remain unclear. Using an instructed-delay reaching task in monkeys, we identified two components in population responses spanning PMd and M1. A “dedicated” component, which segregated activity at the level of individual units, emerged in PMd during preparation. It was most prominent following movement when M1 became strongly engaged, and principally involved the contralateral hemisphere. In contrast to recent reports, these dedicated signals solely accounted for divergence of arm-specific neural subspaces. The other “distributed” component mixed signals for each arm within units, and the subspace containing it did not discriminate between arms at any stage. The statistics of the population response suggest two functional aspects of the cortical network: one that spans both hemispheres for supporting preparatory and ongoing processes, and another that is predominantly housed in the contralateral hemisphere and specifies unilateral output.

Oral dyspraxia in self-limited epilepsy with centrotemporal spikes: a comparative study with a control group

ABSTRACT Background: self-limited epilepsy with centrotemporal spikes, previously considered benign focal childhood epilepsy with centrotemporal spikes show clinical signs of involvement of Rolandic areas, mainly lower area, which may affect the planning and execution of motor sequences. Objective: This study aimed to evaluated oral praxis in children with self-limited epilepsy with centrotemporal spikes and compare to the age-matched control group. Methods: This was a descriptive study with 74 children with self-limited epilepsy with centrotemporal spikes, with the classical forms according to International League Against Epilepsy, and between 4 and 15 years of age, selected from the child neurology outpatient clinic of the Hospital das Clínicas, Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil, and 239 age-matched and educational level-matched (convenience sampling) control children. All children were submitted to the battery of oral volitional movements, which consisted of 44 tests for oral movement (tongue, lip, cheek, jaw, and palate) and 34 phonemes and consonant cluster tasks, with simple and sequenced oral movements. Results: The mean age and standard deviation (SD) of children with epilepsy was 9.08 years (SD 2.55) and of controls 9.61 years (SD 3.12). The results showed significant differences between the groups with a poorer performance of children with epilepsy compared to children without epilepsy in simple and particularly in sequenced movements. Conclusion: These findings can be attributed to the genetically determined immaturity of cortical structures related to motor planning in children with self-limited epilepsy with centrotemporal spikes.

Modulation of initial movement for double potential targets with specific time constraints

In goal-directed behavior, individuals are often required to plan and execute a movement with multiple competing reach targets simultaneously. The time constraint assigned to the target is an important factor that affect the initial movement planning, but the adjustments made to the starting behavior considering the time constraints specific to each target have not yet been clarified. The current study examined how humans adjusted their motor planning for double potential targets with independent time constraints under a go-before-you-know situation. The results revealed that the initial movements were modulated depending on the time constraints for potential targets. However, under tight time constraints, the performance in the double-target condition was lower than the single-target condition, which was a control condition implemented to estimate performance when one target is ignored. These results indicate that the initial movement for multiple potential targets with independent time constraints can be modified, but the planning is suboptimal.

An evaluation of language in brain tumour patients using a new cognitive-motivated testing protocol

<p>In patients undergoing tumour resection surgery, assessment of language is vital, given its crucial role in everyday social functioning. However, despite the unique neuropathological mechanisms in tumours, current literature presents variable results regarding language capabilities in this population. In this thesis we have developed a new neuropsychological test battery, the Brief Language Assessment for Surgical Tumours (BLAST), to specifically evaluate language in brain tumour patients. The BLAST adopts a core skills approach, which identifies and examines 11 core cognitive skills that have been derived based on current cognitive and psycholinguistic theories, and are required for everyday language processing. In this study, we administered the BLAST to a cohort of 40 undifferentiated tumour surgery patients, both pre and postoperatively. Also tested were 60 healthy controls categorised into three age groups (18-29, 30-50 and 51+years). We examined various aspects of overall test performance in order to evaluate: 1) the overall sensitivity of the test battery at detecting abnormalities in this population; 2) selectivity: the relative incidence of impairments across the various subtests; and 3) their sensitivity to change following surgery. We also explored the effects of lesion localisation and other lesion characteristics (malignancy, oedema and volume) on test performance. Following this, we then used participants' test performance to create operationalised measures of our 11 core cognitive skills, and evaluated these measures in a similar way to the basic test scores. Finally, we used Voxel-Based Lesion Symptom Mapping to determine the specific anatomical predictors for each core cognitive skill score. When investigating overall task performance, we found that 94% of preoperative patients and 90% of postoperative patients were impaired in at least one task within the BLAST. Also, 65% and 68% of patients had impaired scores on at least one core skill preoperatively and postoperatively respectively. It was also found that the core skills measures were effective at discriminating amongst different neurological profiles. Specifically, patients with a left posterior tumour had significantly lower scores than other groups on measures of accessing semantic knowledge, lexical selection and phonological encoding, either pre or postoperatively, or both. Conversely, patients with a left frontal tumour had significantly lower scores on measures of articulatory motor planning and verb retrieval. Our Voxel-Lesion-Symptom-Mapping analysis corroborated these findings. Lesions within the left superior temporal lobe significantly predicted lows scores in accessing semantic knowledge, lexical selection and phonological encoding. Conversely, lesions within the left inferior, as well as the superior posterior frontal lobe, significantly predicted low scores on goal-driven response selection, articulatory-motor planning and verb retrieval. We conclude that a core skills approach may be a more effective means of assessing language in tumour populations than more conventional tools that emphasise overall task performance. Such derived measures are sensitive to impairments in this population, and are less likely to be confounded by nonlinguistic impairments that can impact significantly on overall task scores. They may also be useful in guiding postoperative rehabilitation. Further, the scores derived here are associated with quite specific neural substrates, making them potentially useful in guiding surgery and reducing postoperative linguistic deficits. Finally, we conclude that the investigation of tumour populations can also provide unique theoretical insights into language processing and its neural underpinnings in its own right.</p>