Cognitive models and biology of auditory hallucinations

The psycho-periodic cube

The current diagnostic classification systems in psychiatry have been developed primarily for evidence-based clinical decision making with both categorical and dimensional approaches having their own advantages and disadvantages. Efforts have been made to improve these classification systems, and we are now at the point where we must expand beyond the one-dimensionality of these systems. In this paper, we propose that psychiatric disorders can be arranged in a three-dimensional classification system according to the degree of dysfunctions on three specific axes in a way that is similar to the arrangement of chemical elements according to their atomic weights in Mendeleyev's periodic table. For the three axes, we chose externalization, drive, and attention to represent the three-dimensional descriptions of mental health, namely, well-being in social, motivational, and cognitive areas, respectively. Throughout the paper, we explain our reasons for choosing these three axes and compare our hypothesis with categorical diagnostic systems as well as Cloninger's dimensional diagnostic system using personality disorders, affective disorders, and schizophrenia as the specific diagnostic samples.

Tricks of the mind: Visual hallucinations as disorders of attention

Visual hallucinations are common across a number of disorders but to date, a unifying pathophysiology underlying these phenomena has not been described. In this manuscript, we combine insights from neuropathological, neuropsychological and neuroimaging studies to propose a testable common neural mechanism for visual hallucinations. We propose that 'simple' visual hallucinations arise from disturbances within regions responsible for the primary processing of visual information, however with no further modulation of perceptual content by attention. In contrast, 'complex' visual hallucinations reflect dysfunction within and between the Attentional Control Networks, leading to the inappropriate interpretation of ambiguous percepts. The incorrect information perceived by hallucinators is often differentially interpreted depending on the time-course and the neuroarchitecture underlying the interpretation. Disorders with 'complex' hallucinations without retained insight are proposed to be associated with a reduction in the activity within the Dorsal Attention Network. The review concludes by showing that a variety of pathological processes can ultimately manifest in any of these three categories, depending on the precise location of the impairment.