Academic journal article Cognitive, Affective and Behavioral Neuroscience

Differential Activation Patterns of Occipital and Prefrontal Cortices during Motion Processing: Evidence from Normal and Schizophrenic Brains

Academic journal article Cognitive, Affective and Behavioral Neuroscience

Differential Activation Patterns of Occipital and Prefrontal Cortices during Motion Processing: Evidence from Normal and Schizophrenic Brains

Article excerpt

Visual motion perception is normally mediated by neural processing in the posterior cortex. Focal damage to the middle temporal area (MT), a posterior extrastriate region, induces motion perception impairment. It is unclear, however, how more broadly distributed cortical dysfunction affects this visual behavior and its neural substrates. Schizophrenia manifests itself in a variety of behavioral and perceptual abnormalities that have proved difficult to understand through a dysfunction of any single brain system. One of these perceptual abnormalities involves impaired motion perception. Motion processing provides an opportunity to clarify the roles of multiple cortical networks in both healthy and schizophrenic brains. Using fMRI, we measured cortical activation while participants performed two visual motion tasks (direction discrimination and speed discrimination) and one nonmotion task (contrast discrimination). Normal controls showed robust cortical activation (BOLD signal changes) in MT during the direction and speed discrimination tasks, documenting primary processing of sensory input in this posterior region. In patients with schizophrenia, cortical activation was significantly reduced in MT and significantly increased in the inferior convexity of the prefrontal cortex, an area that is normally involved in higher level cognitive processing. This shift in cortical responses from posterior to prefrontal regions suggests that motion perception in schizophrenia is associated with both deficient sensory processing and compensatory cognitive processing. Furthermore, this result provides evidence that in the context of broadly distributed cortical dysfunction, the usual functional specificity of the cortex becomes modified, even across the domains of sensory and cognitive processing.

Functional specificity is a fundamental property of brain-behavior relationships (Brodmann, 1909; Edelman, 2003; Goldman-Rakic, 1988; Van Essen & Maunsell, 1983). The posterior cortex, for instance, mediates primarily sensory processes, whereas the anterior cortex mediates primarily cognitive processes. The cortex is also plastic, in that it can adjust its functionality to adapt to changes in its own system and in the external world. For example, focal damage to motion-sensitive areas (such as the middle temporal area, or MT) induces an acute deficit in motion perception (Newsome & Pare, 1988), an example of functional specificity between the posterior cortex and sensory responses. This induced perceptual deficit can recover over time, when other parts of the same cortical area adjacent to the focal damage are recruited (Plant & Nakayama, 1993; Wurtz, Yamasaki, Duffy, & Roy, 1990).

Research on visual motion processing has focused primarily on the occipital cortex, because motion perception has generally been considered a task mediated in regions such as MT. However, several lines of evidence have recently made it clear that the prefrontal cortex (PFC) also participates in neural responses to motion stimuli. First, neural responses in the PFC are not only sensitive to the presence of moving targets, but are also modulated by the specifics of motion task demands (Zaksas & Pasternak, 2006). Second, there is a reciprocal relationship between motion signal strength and neural activity in anterior and posterior regions: Anterior cortical activity decreases, and posterior cortical activity increases, as a function of the strength of motion stimuli (Rees, Friston, & Koch, 2000). The PFC is likely part of a default-mode network, showing deactivation during a low-load task or during resting conditions (Greicius & Menon, 2004). It remains unknown, however, whether these functional roles of the PFC change when sensory processing of motion information in the occipital cortex is deficient.

A more general question concerns the relationship between dysfunction involving more broadly distributed cortical networks, which are strongly implicated in schizophrenia (Andreasen, 1999; Coyle, 1996), and specific behaviors (e. …

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