Trends in Neurosciences
Volume 23, Issue 9, 1 September 2000, Pages 412-417
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Review
Negative symptoms: the ‘pathology’ of motivation and goal-directed behaviour

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Abstract

In many neurological and psychiatric disorders, including Alzheimer’s disease and schizophrenia, symptoms are present that appear to reflect an essential absence of normal movement, cognition and emotional states. These negative symptoms might reflect fundamental impairments in basic brain mechanisms that underlie goal-directed behaviour. Knowledge of the pathology and pathophysiology of these diseases, combined with evidence from basic science, offers opportunities for understanding the neurobiological basis of goal-directed behaviour, particularly the interaction between limbic structures and striato-thalamo-cortical circuits. The study of patients with negative symptoms also provides opportunities for testing cognitive models of goal-directed behaviour, and eventually to map such models onto the neurobiology of both normal and abnormal behaviour.

Section snippets

Phenomenology of negative symptoms and apathy

The term ‘negative symptoms’ has its origins in the writings of Hughlings-Jackson2, and his distinction between positive or ‘florid’ symptoms, and negative or ‘defect’ symptoms. Negative symptoms resulted from a true loss of function, whereas positive symptoms represented the disorganization or exaggeration of existing functions. It was in relation to schizophrenia that negative symptoms found a modern home, as a reworking of Bleuler’s original description of the disease ‘Many schizophrenics

Negative symptoms and apathy in neurological disorders

Recent case reports and series (for example 6, 7), plus group studies that used standardized instruments such as the SANS, Apathy Evaluation Scale (AES)8 and Neuropsychiatric Inventory (NPI)9 have greatly increased our appreciation of the widespread occurrence of apathy or negative symptoms in neurological disorders (Table 2).

As with negative symptoms in schizophrenia, doubts are often raised about the status of apathy as a distinct neurobehavioural phenomenon separate from other symptoms,

Neurobiological substrate of apathy and negative symptoms

Table 2 reveals a high prevalence of apathy or negative symptoms in patients with pathology involving the frontal cortex and subcortical structures, particularly those with prototypical fronto-subcortical dementia syndromes26, such as progressive supranuclear palsy (PSP) and frontal lobe dementia. There is no evidence that damage to any one structure, pathway or region is uniquely responsible for producing apathy or negative symptoms. Instead, a network of cortical and subcortical areas is

Goal-directed behaviour and motivation

Although we might appreciate the phenomenology of negative symptoms and have some idea of their possible neurobiological substrate, we lack a framework of the normal cognitive processes that are involved. One such framework is explicit in the Marin formulation of apathy; that it is a reduction in GDB owing to impaired motivation5.

Within neuroscience, the construct of GDB is increasingly being used to operationalize a broad spectrum of purposeful actions and their determinants, from the simplest

Concluding remarks

The GDB model, although complex, serves to highlight the differences between simple movement and purposeful GDB. It places cognitive, motor, emotional and motivational processes within an overall system that subserves GDB and helps to oppose the tendency to view such processes in isolation. It is obviously tempting to map the motivational, emotional, cognitive and motor components of such a model to the neuronal structures and circuits outlined in Fig. 1. For example, it is relatively easy to

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