Action execution and recognition: a neuropsychological analysis

Humans appear to show an innate tendency to imitate, and this may provide one of the foundations of social communication. Several studies have been carried out in social and cognitive science in order to understand how imitation works, which parts of the brain are involved, and what the role of imitation might be in social behaviour. Previous brain imaging and neuropsychological studies report data that favour a dual process account of imitation, according to which actions are imitated through different mechanisms on the basis of whether they are meaningful and familiar (MF actions) or meaningless/unfamiliar (ML actions). However many questions remain to be clarified – such as which brain areas mediate these different actions. In addition to the distinction between MF and ML gestures, there is considerable interest in the production of different types of known gestures – particularly between actions involving tools (i.e. transitive actions) and those subserving communicative (intransitive) gestures, and in how the production of these gestures relates to the processes involved in recognizing the gestures as input. This thesis reports a neuropsychological examination of the functional and neural bases of imitation using converging data from behavioural studies with different patient groups (stroke patients, patients with Parkinson’s Disease, PD) and structural brain imaging (particularly using voxel-based morphometric [VBM] analyses) to examine lesion-symptom relations. The first empirical chapter (Chapter 2) describes a neuropsychological study on the recognition and production of MF actions and the imitation of ML gestures, in patients with unilateral left or rightside brain damage (respectively: LBD and RBD patients). At a group level, LBD patient were worse in imitation than RBD patients only when novel transitive actions had to be reproduced, when both LBD and RBD differed from healthy participants, while intransitive gestures were generally easier to be executed. Also both transitive and intransitive action imitation tasks were correlated to action recognition. At a single subject level, however, there was evidence for some dissociated symptoms, suggesting that at least partially different mechanisms mediate the imitation of transitive and intransitive gestures and gesture production as opposed to recognition. Chapter 3 presents a first attempt to use VBM to evaluate the relations between brain lesions and the symptoms of apraxia, contrasting the imitation of meaningful (familiar) and meaningless (unfamiliar) transitive and intransitive actions in a consecutive series of brain damaged patients. Chapters 4 and 5 describe two investigations where VBM was again used in a large-scale lesionsymptom analysis of deficits in i) the recognition and generation to command of MF actions and the imitation of ML actions, and ii) the generation to command of different types of learned action (transitive or intransitive gestures). All three investigations using VBM revealed common and differential neural substrates involved in the execution of the tasks considered, and the data are compatible with a model which posits that different processes are involved in MF and ML action execution, as well as in action understanding. The results also suggest that the distinction between transitive and intransitive actions may be included in an action reproduction system. In the final empirical chapter (Chapter 6), I report a study on PD patients tested for imitation of transitive and intransitive MF and ML actions, also relating their performance to the neurological/peripheral symptoms of the disease. This study revealed that PD patients were impaired in imitation, and they also had different pattern of deficit for transitive and intransitive actions. The correlation with peripheral symptoms was not significant, though there were correlations with underlying cognitive processes likely to support action production. Chapter 7 summarizes the different results and links them back to functional and neural accounts of action recognition, production and imitation. The relations between action production and recognition and other cognitive processes are discussed, as are methodological issues concerning lesion-symptom mapping

Consciousness and the prefrontal parietal network: insights from attention, working memory, and chunking

Consciousness has of late become a “hot topic” in neuroscience. Empirical work has centered on identifying potential neural correlates of consciousness (NCCs), with a converging view that the prefrontal parietal network (PPN) is closely associated with this process. Theoretical work has primarily sought to explain how informational properties of this cortical network could account for phenomenal properties of consciousness. However, both empirical and theoretical research has given less focus to the psychological features that may account for the NCCs. The PPN has also been heavily linked with cognitive processes, such as attention. We describe how this literature is under-appreciated in consciousness science, in part due to the increasingly entrenched assumption of a strong dissociation between attention and consciousness. We argue instead that there is more common ground between attention and consciousness than is usually emphasized: although objects can under certain circumstances be attended to in the absence of conscious access, attention as a content selection and boosting mechanism is an important and necessary aspect of consciousness. Like attention, working memory and executive control involve the interlinking of multiple mental objects and have also been closely associated with the PPN. We propose that this set of cognitive functions, in concert with attention, make up the core psychological components of consciousness. One related process, chunking, exploits logical or mnemonic redundancies in a dataset so that it can be recoded and a given task optimized. Chunking has been shown to activate PPN particularly robustly, even compared with other cognitively demanding tasks, such as working memory or mental arithmetic. It is therefore possible that chunking, as a tool to detect useful patterns within an integrated set of intensely processed (attended) information, has a central role to play in consciousness. Following on from this, we suggest that a key evolutionary purpose of consciousness may be to provide innovative solutions to complex or novel problems

Lesions impairing regular versus irregular past tense production

We investigated selective impairments in the production of regular and irregular past tense by examining language performance and lesion sites in a sample of twelve stroke patients. A disadvantage in regular past tense production was observed in six patients when phonological complexity was greater for regular than irregular verbs, and in three patients when phonological complexity was closely matched across regularity. These deficits were not consistently related to grammatical difficulties or phonological errors but were consistently related to lesion site. All six patients with a regular past tense disadvantage had damage to the left ventral pars opercularis (in the inferior frontal cortex), an area associated with articulatory sequencing in prior functional imaging studies. In addition, those that maintained a disadvantage for regular verbs when phonological complexity was controlled had damage to the left ventral supramarginal gyrus (in the inferior parietal lobe), an area associated with phonological short-term memory. When these frontal and parietal regions were spared in patients who had damage to subcortical (n = 2) or posterior temporo-parietal regions (n = 3), past tense production was relatively unimpaired for both regular and irregular forms. The remaining (12th) patient was impaired in producing regular past tense but was significantly less accurate when producing irregular past tense. This patient had frontal, parietal, subcortical and posterior temporo-parietal damage, but was distinguished from the other patients by damage to the left anterior temporal cortex, an area associated with semantic processing. We consider how our lesion site and behavioural observations have implications for theoretical accounts of past tense production

Explaining semantic short-term memory deficits:evidence for the critical role of semantic control

Patients with apparently selective short-term memory (STM) deficits for semantic information have played an important role in developing multi-store theories of STM and challenge the idea that verbal STM is supported by maintaining activation in the language system. We propose that semantic STM deficits are not as selective as previously thought and can occur as a result of mild disruption to semantic control processes, i.e., mechanisms that bias semantic processing towards task-relevant aspects of knowledge and away from irrelevant information. We tested three semantic STM patients with tasks that tapped four aspects of semantic control: (i) resolving ambiguity between word meanings, (ii) sensitivity to cues, (iii) ignoring irrelevant information and (iv) detecting weak semantic associations. All were impaired in conditions requiring more semantic control, irrespective of the STM demands of the task, suggesting a mild, but task-general, deficit in regulating semantic knowledge. This mild deficit has a disproportionate effect on STM tasks because they have high intrinsic control demands: in STM tasks, control is required to keep information active when it is no longer available in the environment and to manage competition between items held in memory simultaneously. By re-interpreting the core deficit in semantic STM patients in this way, we are able to explain their apparently selective impairment without the need for a specialised STM store. Instead, we argue that semantic STM patients occupy the mildest end of spectrum of semantic control disorders

Language and thought are not the same thing: evidence from neuroimaging and neurological patients

Is thought possible without language? Individuals with global aphasia, who have almost no ability to understand or produce language, provide a powerful opportunity to find out. Surprisingly, despite their near-total loss of language, these individuals are nonetheless able to add and subtract, solve logic problems, think about another person's thoughts, appreciate music, and successfully navigate their environments. Further, neuroimaging studies show that healthy adults strongly engage the brain's language areas when they understand a sentence, but not when they perform other nonlinguistic tasks such as arithmetic, storing information in working memory, inhibiting prepotent responses, or listening to music. Together, these two complementary lines of evidence provide a clear answer: many aspects of thought engage distinct brain regions from, and do not depend on, language

Revisiting working memory: Are domain, process and global models mutually exclusive, nested or orthogonal?

Working memory (WM) is a cognitive function whereby task-relevant information is actively maintained and manipulated in mind for goal-directed behaviour. Three competing models, here dubbed the global, domain and process models, have attempted to explain its neural underpinnings. Despite extensive research however, no consensus has been reached. Here, we use two new WM paradigms to demonstrate that all three models are partially correct. In the first experiment, our results show that selected frontoparietal regions (MD), from the global model, are largely stimulus-independent. However, more posterior and caudal frontoparietal regions show stimulus-dependent activations as described by the domain model. In the second experiment, our results reveal that a dorsal MD sub-network is more active when information is manipulated, as described by the process model. Thus, WM is best represented by all three models, with the process model nested within the global, and the domain model partially independent from the others

The Neuroscience of Mathematical Cognition and Learning

The synergistic potential of cognitive neuroscience and education for efficient learning has attracted considerable interest from the general public, teachers, parents, academics and policymakers alike. This review is aimed at providing 1) an accessible and general overview of the research progress made in cognitive neuroscience research in understanding mathematical learning and cognition, and 2) understanding whether there is sufficient evidence to suggest that neuroscience can inform mathematics education at this point. We also highlight outstanding questions with implications for education that remain to be explored in cognitive neuroscience. The field of cognitive neuroscience is growing rapidly. The findings that we are describing in this review should be evaluated critically to guide research communities, governments and funding bodies to optimise resources and address questions that will provide practical directions for short- and long-term impact on the education of future generations