The physiology of motor delusions in anosognosia for hemiplegia: Implications for current models of motor awareness

Right brain damaged patients sometimes deny that their left arm is paralysed or even claim to have just moved it. This condition is known as anosognosia for hemiplegia (AHP). Here, we used fMRI to study patients with and without AHP during the execution of a motor task. We found that the delusional belief of having moved was preceded by brain activation of the cortical regions that are implicated in motor control in the left intact hemisphere and in the spared motor regions of the right hemisphere; patients without anosognosia did not present with the same degree of activation. We conclude that the false belief of movement is associated with a combination of strategically placed brain lesions and the preceding residual neural activity of the fronto-parietal motor network. These findings provide evidence that the activity of motor cortices contributes to our beliefs about the state of our motor system.     

Neural localization of semantic context effects in electromagnetic and hemodynamic studies

Measures of electrical brain activity (event-related potentials, ERPs) have been useful in understanding language processing for several decades. Extant data suggest that the amplitude of the N400 component of the ERP is a general index of the ease or difficulty of retrieving stored conceptual knowledge associated with a word, which is dependent on both the stored representation itself, and the retrieval cues provided by the preceding context. Recordings from patients with brain damage, intracranial recordings, and magnetoencephalographic data implicate a (probably large portion of) the left temporal lobe as the largest source of the N400 semantic context effect, with a substantial but lesser contribution from the right temporal lobe. Event-related functional magnetic resonance (fMRI) studies using semantic context manipulations are dominated by observations of greater hemodynamic activity for incongruent sentence completions or semantically unrelated words than congruent or related words, consistent with the direction of the ERP effect. The locations of the hemodynamic effects show some variability across studies, but one commonly identified region is the left superior temporal gyrus, which is compatible with the electrophysiological results. A second commonly identified region in the fMRI studies is the left inferior frontal gyrus, which does not appear to make a substantial contribution to the N400 effect.     

Comparison of hemispheric activation during mental word and rhyme generation using transcranial Doppler sonography

The Wada test is at present the method of choice for preoperative assessment of patients who require surgery close to cortical language areas. It is, however, an invasive test with an attached morbidity risk. By now, an alternative to the Wada test is to combine a lexical word generation paradigm with non-invasive imaging techniques. However, results of this approach are still not in complete agreement with the findings of the Wada test (r = .92; Knecht, Deppe, Ebner et al., 1998). We attempted to obtain a more distinct language lateralization with the development of a phonological rhyme generation paradigm based on pseudoword stimuli. To examine the predictive value of both paradigms we performed simultaneous bilateral functional transcranial Doppler ultrasonography on 19 right-handed male native German subjects. The rhyme generation condition produced a significantly stronger lateralization to the supposed hemisphere of language dominance than the classical word generation condition. The observed differences suggest that the rhyme generation paradigm is more robust in detecting hemispheric language dominance than other neuropsychological paradigms and might be most valuable for preoperative assessment of cortical language areas.     

Does functional neuroimaging solve the questions of neurolinguistics?

Neurolinguistic research has been engaged in evaluating models of language using measures from brain structure and function, and/or in investigating brain structure and function with respect to language representation using proposed models of language. While the aphasiological strategy, which classifies aphasias based on performance modality and a few linguistic variables, has been the most stable, cognitive neurolinguistics has had less success in reliably associating more elaborately proposed levels and units of language models with brain structure. Functional imaging emerged at this stage of neurolinguistic research. In this review article, it is proposed that the often-inconsistent superfluity of outcomes arising from functional imaging studies of language awaits adjustment at both "ends" of the process: model and data. Assumptions that our current language models consistently and reliably represent implicit knowledge within human cerebral processing are in line for major revision; and the promise of functional brain imaging to reveal any such knowledge structures must incorporate stable correlates of the imaging signal as dependent variable.     

Generative models, brain function and neuroimaging

The representational capacity and inherent function of any neuron, neuronal population or cortical area in the brain is dynamic and context-sensitive. Functional integration, or interactions among brain systems, that employ driving (bottom up) and backward (top-down) connections, mediate this adaptive and contextual specialisation. A critical consequence is that neuronal responses, in any given cortical area, can represent different things at different times. This can have fundamental implications for the design of brain imaging experiments and the interpretation of their results. Our arguments are developed under generative models of brain function, where higher-level systems provide a prediction of the inputs to lower-level regions. Conflict between the two is resolved by changes in the higher-level representations, which are driven by the ensuing error in lower regions, until the mismatch is "cancelled". From this perspective the specialisation of any region is determined both by bottom-up driving inputs and by top-down predictions. Specialisation is therefore not an intrinsic property of any region but depends on both forward and backward connections with other areas. Because the latter have access to the context in which the inputs are generated they are in a position to modulate the selectivity or specialisation of lower areas. The implications for classical models (e.g., classical receptive fields in electrophysiology, classical specialisation in neuroimaging and connectionism in cognitive models) are severe and suggest these models may provide incomplete accounts of real brain architectures. Here we focus on the implications for cognitive neuroscience in the context of neuroimaging.     

Functional integration and the mind

Different cognitive functions recruit a number of different, often overlapping, areas of the brain. Theories in cognitive and computational neuroscience are beginning to take this kind of functional integration into account. The contributions to this special issue consider what functional integration tells us about various aspects of the mind such as perception, language, volition, agency, and reward. Here, I consider how and why functional integration may matter for the mind; I discuss a general theoretical framework, based on generative models, that may unify many of the debates surrounding functional integration and the mind; and I briefly introduce each of the contributions.     

Hemispheric asymmetries in visual word-form processing: progress, conflict, and evaluating theories

The ubiquitous left-hemisphere advantage in visual word processing can be accounted for in different ways. Competing theories have been tested recently using cAsE-aLtErNaTiNg words to investigate boundary conditions for the typical effect. We briefly summarize this research and examine the disagreements and commonalities across the theoretical perspectives. This work may provide a good example why a multi-level, multi-method, and multi-paradigm approach holds the greatest promise for rapid theoretical progress.     

Aggression and school social dynamics: The good, the bad, and the ordinary

A social dynamics perspective of aggression in school is presented. This framework focuses on the role of natural social processes in the establishment and maintenance of aggressive behavior in the school context. The five articles in this special issue are briefly reviewed and a synthesis of their contributions for understanding the social dynamics of aggression in school is underscored. Future research and intervention implications are also discussed. The need for examining the role of school social dynamics in conducting social skills interventions, functional behavioral assessments, and the development of positive behavioral support plans is emphasized.