Handwritten Geometrical Patterns in the Evaluation of Motor Symptoms in Psychotic Disorders.

The analysis of handwriting has been used in several contexts. For example, handwriting has shown to be of value in the study of motor symptoms in neurological and mental disorders. In the present work, the geometric analysis of handwriting patterns is proposed as a tool to evaluate motor symptoms in psychotic disorders. Specifically, we have employed the lacunarity, a measure of the heterogeneity of a spatial structure. Forty-two patients with a psychotic disorder and 35 matched healthy controls participated in the study. Participants were asked to copy some patterns with a pen on a white paper. The results showed that lacunarity was significantly higher in handwritten patterns from patients than from controls. In addition, we found higher values of lacunarity in handwritten patterns from patients with severe motor symptoms in comparison with patients with mild or absent motor symptoms. Lacunarity of handwritten patterns was significantly correlated with clinical scores of rigidity. In conclusion we argue that the heterogeneity of handwritten patterns could be used as a simple and objective measure of motor symptoms.

Introspective and Neurophysiological Measures of Mind Wandering in Schizophrenia.

Patients with schizophrenia have often been considered to be "in their own world". However, this casual observation has not been proven by scientific evidence so far. This can be explained because scientific research has usually addressed cognition related to the processing of external stimuli, but only recently have efforts been made to explain thoughts, images and feelings not directly related to the external environment. This internally directed cognition has been called mind wandering. In this paper, we have explored mind wandering in schizophrenia under the hypothesis that a predominance of mind wandering would be a core dysfunction in this disorder. To this end, we collected verbal reports and measured electrophysiological signals from patients with schizophrenia spectrum disorders and matched healthy controls while they were presented with segments of films. The results showed that mind wandering was more frequent in patients than in controls. This higher frequency of mind wandering did not correlate with deficits in attentional, memory or executive functioning. In addition, mind wandering in patients was characterized by a different pattern of Electroencephalography (EEG) complexity in patients than in controls, leading to the suggestion that mind wandering in schizophrenia could be of a different nature. These findings could have relevant implications for the conceptualization of this severe mental disorder.

Fractal dimension analysis of states of consciousness and unconsciousness using transcranial magnetic stimulation.

BACKGROUND AND OBJECTIVE: Knowing whether a subject is conscious or not is a current challenge with a deep potential clinical impact. Recent theoretical considerations suggest that consciousness is linked to the complexity of distributed interactions within the corticothalamic system. The fractal dimension (FD) is a quantitative parameter that has been extensively used to analyse the complexity of structural and functional patterns of the human brain. In this study we investigate FD to assess whether it can discriminate between consciousness and different states of unconsciousness in healthy individuals. METHODS: We study 69 high-density electroencephalogram (hd-EEG) measurements after transcranial magnetic stimulation (TMS) in 18 healthy subjects progressing from wakefulness to non-rapid eye movement (NREM) sleep and sedation induced by different anaesthetic agents (xenon and propofol). We quantify the integration of thalamocortical networks by calculating the FD of a spatiotemporal voxelization obtained from the locations of all sources that are significantly activated by the perturbation (4DFD). Moreover, we study the temporal evolution of the evoked spatial distributions and compute a measure of the differentiation of the response by means of the Higuchi FD (HFD). Finally, a Fractal Dimension Index (FDI) of perturbational complexity is computed as the product of both quantities: integration FD (4DFD) and differentiation FD (HFD). RESULTS: We found that FDI is significantly lower in sleep and sedation when compared to wakefulness and provides an almost perfect intra-subject discrimination between conscious and unconscious states. CONCLUSIONS: These results support the combination of FD measures of cortical integration and cortical differentiation as a novel paradigm of tracking complex spatiotemporal dynamics in the brain that could provide further insights into the link between complexity and the brain's capacity to sustain consciousness.

Spatial Analysis of Handwritten Texts as a Marker of Cognitive Control.

We explore the idea that cognitive demands of the handwriting would influence the degree of automaticity of the handwriting process, which in turn would affect the geometric parameters of texts. We compared the heterogeneity of handwritten texts in tasks with different cognitive demands; the heterogeneity of texts was analyzed with lacunarity, a measure of geometrical invariance. In Experiment 1, we asked participants to perform two tasks that varied in cognitive demands: transcription and exposition about an autobiographical episode. Lacunarity was significantly lower in transcription. In Experiment 2, we compared a veridical and a fictitious version of a personal event. Lacunarity was lower in veridical texts. We contend that differences in lacunarity of handwritten texts reveal the degree of automaticity in handwriting.

Fractal characterization of internally and externally generated conscious experiences.

Although there is an extensive literature on the study of the neural correlates of consciousness (NCC) this is a subject that is far from being considered over. In this paper we present a novel experimental paradigm, based on binocular rivalry, to study internally and externally generated conscious experiences. We called this procedure bimodal rivalry. In addition, and assuming the non-linear nature of the EEG signals, we propose the use of fractal dimension to characterize the complexity of the EEG signal associated with each percept. Analysis of the data showed a significant difference in complexity between the internally generated and externally generated percepts. Moreover, EEG complexity was dissimilar for externally generated auditory and visual percepts. These results support fractal dimension analyses as a new tool to characterize conscious perception.