Exploring the interplay between brain and mind in Alzheimer's disease

The mechanisms behind the interplay between brain structure, function and cognition are, fundamentally, still unknown. On one hand, there is evidence that damages to brain structure affect its function and, as a consequence, cognitive processes. On the other hand, there is also convincing evidence that altered cognitive processes can influence the structure of the human brain. In most clinical cases, this lack of knowledge makes it difficult to characterize in time an ongoing disease or to identify early warning signals of neurodegenerative diseases and psychiatric disorders in healthy subjects, with obvious limitations to prevention and treatment. Interestingly, there is increasing evidence for speech disorder and language alteration in humans affected by neurodegenerative diseases and psychiatric disorders.
The tight relationship between brain and mind is further strengthened by recent studies which proved the existence of semantic maps tiling the human cerebral cortex [1]. Organization of language and exploration of concepts in human mind are usually represented by cognitive units, namely the concepts, linked together by associative relationships which form semantic networks or clusters. However, understanding how humans navigate such networks remains elusive, because the underlying topology of concepts can not be observed directly and only functional representations are accessible. Here, we overcome those limitations and show that the hypothesis of an underlying, latent, geometry characterizing the human mind is plausible. We characterize this geometry by means of adequate descriptors for exploring and navigating dynamics, demonstrating that they are able to capture the differences between healthy subjects and patients at different stages of dementia, namely mild cognitive impairment and Alzheimer's disease. We present preliminary results from a joint
collaboration with the Department of Mental Health of health services agency of the Trento Province (APSS), that aims at integrating the neuro-psychological analysis of individuals affected by Alzheimer's disease to enrich the clinical assessment with information provided by mental pathways - sequential associations of concepts - and their altered navigation. Given the complex nature of the system in question, after investigating the potential latent geometry of semantic space, we propose to explore the mental navigation strategies and the emerging pathways by leveraging the network approach. We assume that concepts in the human mind are cognitive units (nodes) connected with each other by semantic links, as
suggested by Collins and Quillian almost fifty years ago, and that the navigation of the corresponding cognitive network can be used to gain insight about the disease dynamics. Our work capitalizes on recent studies relating, for instance, abnormal priming in Alzheimer's patients to the degradation of their cognitive network [2]. To this aim, we use existing word embeddings [3] made for the Italian language [4] and patient clinical data collected at APSS. Our results provide a new unifying conceptual and computational framework, that can also be used to assess neurodegenerative diseases from language and semantic memory retrieval tasks resulting in a more complete, mathematical and data-driven output.