Philipp Kellmeyer

Ventral and dorsal pathways for language

Built on an analogy between the visual and auditory systems, the following dual stream model for language processing was suggested recently: a dorsal stream is involved in mapping sound to articulation, and a ventral stream in mapping sound to meaning. The goal of the study presented here was to test the neuroanatomical basis of this model. Combining functional magnetic resonance imaging (fMRI) with a novel diffusion tensor imaging (DTI)-based tractography method we were able to identify the most probable anatomical pathways connecting brain regions activated during two prototypical language tasks. Sublexical repetition of speech is subserved by a dorsal pathway, connecting the superior temporal lobe and premotor cortices in the frontal lobe via the arcuate and superior longitudinal fascicle. In contrast, higher-level language comprehension is mediated by a ventral pathway connecting the middle temporal lobe and the ventrolateral prefrontal cortex via the extreme capsule. Thus, according to our findings, the function of the dorsal route, traditionally considered to be the major language pathway, is mainly restricted to sensory-motor mapping of sound to articulation, whereas linguistic processing of sound to meaning requires temporofrontal interaction transmitted via the ventral route.

Combining functional and anatomical connectivity reveals brain networks for auditory language comprehension

Cognitive functions are organized in distributed, overlapping, and interacting brain networks. Investigation of those large-scale brain networks is a major task in neuroimaging research. Here, we introduce a novel combination of functional and anatomical connectivity to study the network topology subserving a cognitive function of interest. (i) In a given network, direct interactions between network nodes are identified by analyzing functional MRI time series with the multivariate method of directed partial correlation (dPC). This method provides important improvements over shortcomings that are typical for ordinary (partial) correlation techniques. (ii) For directly interacting pairs of nodes, a region-to-region probabilistic fiber tracking on diffusion tensor imaging data is performed to identify the most probable anatomical white matter fiber tracts mediating the functional interactions. This combined approach is applied to the language domain to investigate the network topology of two levels of auditory comprehension: lower-level speech perception (i.e., phonological processing) and higher-level speech recognition (i.e., semantic processing). For both processing levels, dPC analyses revealed the functional network topology and identified central network nodes by the number of direct interactions with other nodes. Tractography showed that these interactions are mediated by distinct ventral (via the extreme capsule) and dorsal (via the arcuate/superior longitudinal fascicle fiber system) long- and short-distance association tracts as well as commissural fibers. Our findings demonstrate how both processing routines are segregated in the brain on a large-scale network level. Combining dPC with probabilistic tractography is a promising approach to unveil how cognitive functions emerge through interaction of functionally interacting and anatomically interconnected brain regions.

Damage to ventral and dorsal language pathways in acute aphasia

Converging evidence from neuroimaging studies and computational modelling suggests an organization of language in a dual dorsal–ventral brain network: a dorsal stream connects temporoparietal with frontal premotor regions through the superior longitudinal and arcuate fasciculus and integrates sensorimotor processing, e.g. in repetition of speech. A ventral stream connects temporal and prefrontal regions via the extreme capsule and mediates meaning, e.g. in auditory comprehension. The aim of our study was to test, in a large sample of 100 aphasic stroke patients, how well acute impairments of repetition and comprehension correlate with lesions of either the dorsal or ventral stream. We combined voxelwise lesion-behaviour mapping with the dorsal and ventral white matter fibre tracts determined by probabilistic fibre tracking in our previous study in healthy subjects. We found that repetition impairments were mainly associated with lesions located in the posterior temporoparietal region with a statistical lesion maximum in the periventricular white matter in projection of the dorsal superior longitudinal and arcuate fasciculus. In contrast, lesions associated with comprehension deficits were found more ventral-anterior in the temporoprefrontal region with a statistical lesion maximum between the insular cortex and the putamen in projection of the ventral extreme capsule. Individual lesion overlap with the dorsal fibre tract showed a significant negative correlation with repetition performance, whereas lesion overlap with the ventral fibre tract revealed a significant negative correlation with comprehension performance. To summarize, our results from patients with acute stroke lesions support the claim that language is organized along two segregated dorsal–ventral streams. Particularly, this is the first lesion study demonstrating that task performance on auditory comprehension measures requires an interaction between temporal and prefrontal brain regions via the ventral extreme capsule pathway.

Ventral and dorsal fiber systems for imagined and executed movement

Although motor imagery is an entirely cognitive process, it shows remarkable similarity to overt movement in behavioral and physiological studies. In concordance, brain imaging studies reported shared fronto-parietal sensorimotor networks commonly engaged by both tasks. However, differences in prefrontal and parietal regions point toward additional cognitive mechanisms in the context of imagery. Within the perspective of a general dichotomization into dorsal and ventral processing streams in the brain, the question arises whether motor imagery and overt movement could differentially involve the dorsal or ventral system. Therefore, we combined fMRI and DTI data of 20 healthy subjects to analyze the anatomical characteristics of connecting fronto-parietal association pathways of imagined and overt movements. We found a dichotomy of fiber pathways into dorsal and ventral systems: the superior longitudinal fascicle (SLF II-III) was found to connect frontal and parietal regions involved in both overt and imagined movements, whereas a ventral tract via the extreme/external capsule (EmC/EC) connects cortical regions specific for motor imagery that were situated more anteriorly and posteriorly. We suppose that motor imagery-related kinesthetic emulations are embedded into dorsal sensorimotor networks, and imagery-specific cognitive functions are implemented in the ventral system. These findings have implications for models of motor cognition.

The Effects of Closed-Loop Medical Devices on the Autonomy and Accountability of Persons and Systems.

Closed-loop medical devices such as brain-computer interfaces are an emerging and rapidly advancing neurotechnology. The target patients for brain-computer interfaces (BCIs) are often severely paralyzed, and thus particularly vulnerable in terms of personal autonomy, decisionmaking capacity, and agency. Here we analyze the effects of closed-loop medical devices on the autonomy and accountability of both persons (as patients or research participants) and neurotechnological closed-loop medical systems. We show that although BCIs can strengthen patient autonomy by preserving or restoring communicative abilities and/or motor control, closed-loop devices may also create challenges for moral and legal accountability. We advocate the development of a comprehensive ethical and legal framework to address the challenges of emerging closed-loop neurotechnologies like BCIs and stress the centrality of informed consent and refusal as a means to foster accountability. We propose the creation of an international neuroethics task force with members from medical neuroscience, neuroengineering, computer science, medical law, and medical ethics, as well as representatives of patient advocacy groups and the public.

Four ethical priorities for neurotechnologies and AI

Artificial intelligence and brain–computer interfaces must respect and preserve peoples privacy, identity, agency and equality, say Rafael Yuste, Sara Goering and colleagues.

Fronto-parietal dorsal and ventral pathways in the context of different linguistic manipulations.

This study investigates structural connectivity between left fronto-parietal brain regions that were identified in a previous fMRI study which used different linguistic manipulation tasks. Diffusion-weighted images were acquired from 20 volunteers. Structural connectivity between brain regions from the fMRI study was computed using probabilistic fiber tracking. For suprasegmental manipulation, left inferior parietal lobule (IPL) and left inferior frontal gyrus (IFG), pars opercularis, were connected by a dorsal pathway via the arcuate fascicle and superior longitudinal fascicle III. For segmental manipulation, left IPL and IFG, pars triangularis, were connected by a ventral pathway via the middle longitudinal fascicle and the extreme capsule. We conclude that the dorsal pathway provides a route for mapping from phonological memory in IPL to the inferior frontal articulatory network while the ventral pathway could facilitate the modulation of phonological units based on lexical-semantic aspects, mediate the complexity of auditory objects and the unification of actor-event schemata.

Assessment of the ethical review process for non-pharmacological multicentre studies in Germany on the basis of a randomised surgical trial

Objective: To examine the current ethical review process (ERP) of ethics committees in a non-pharmacological trial from the perspective of a clinical investigator. Design: Prospective collection of data at the Study Centre of the German Surgical Society on the duration, costs and administrative effort of the ERP of a randomised controlled multicentre surgical INSECT Trial (INterrupted or continuous Slowly absorbable sutures—Evaluation of abdominal Closure Techniques Trial, ISRCTN 24023541) between November 2003 and May 2005. Setting: Germany. Participants: 18 ethics committees, including the ethics committee handling the primary approval, responsible overall for 32 clinical sites throughout Germany. 8 ethics committees were located at university medical schools (MSU) and 10 at medical chambers. Duration was measured as days between submission and receipt of final approval, costs in euros and administrative effort by calculation of the product of the total number of different types of documents and the mean number of copies required (primary approval acting as the reference standard). Results: The duration of the ERP ranged from 1 to 176 (median 31) days. The median duration was 26 days at MSUs compared with 34 days at medical chambers. The total cost was €2947. 1 of 8 ethics committees at universities (€250) and 8 of 10 at medical chambers charged a median fee of €162 (mean €269.70). The administrative effort for primary approval was 30. Four ethics committees required a higher administrative effort for secondary approval (37, 39, 42 and 104). Conclusion: The ERP for non-pharmacological multicentre trials in Germany needs improvement. The administrative process has to be standardised: the application forms and the number and content of the documents required should be identical or at least similar. The fees charged vary considerably and are obviously too high for committees located at medical chambers. However, the duration of the ERP was, with some exceptions, excellent. A centralised ethics committee in Germany for multicentre trials such as the INSECT Trial can simplify the ERP for clinical investigators in and outside the country.

Reply to Yamada: The extreme capsule is the ventral pathway for language

In his letter (1), Yamada claims that, in our article (2), we erroneously allocated the ventral pathway for language processing to the extreme capsule (EmC) rather than the external capsule (EC). He argues that, in his data (3), the direction of fibers running in the EmC “is not anteroposterior but rather transverse or superoinferior in the transaxial plane.” Instead, the EC has fibers running in the “anteroposterior direction,” thereby providing the temporo-frontal connection of interest.

Social robots in rehabilitation: A question of trust

Creating and maintaining trust in human-robot interactions should be priorities when designing social robots for rehabilitation. Social robots can help meet the growing need for rehabilitation assistance; measures for creating and maintaining trust in human-robot interactions should be priorities when designing social robots for rehabilitation.