Functional magnetic resonance imaging examination of the magnocellular visual pathway in nonpsychotic relatives of persons with schizophrenia.

Functional magnetic resonance imaging examination of the magnocellular visual pathway in nonpsychotic relatives of persons with schizophrenia Dear Editors, Research in humans and primates has identified two physiological subsystems in the visual system (Living-stone and Hubel, 1987). The magnocellular (M) visual pathway is responsible for processing location information and motion, while the parvocellular (P) visual pathway is responsible for processing detail and color. Psychophysical studies in persons with schizophrenia and their healthy relatives have revealed that the M pathway appears dysfunctional, while the P pathway appears relatively preserved (e. Few physiological studies have examined M pathway functioning in schizophrenia. Three studies using electroencephalography (EEG) reported reduced signal amplitude in posterior cortical regions along the M pathway in persons with schizophrenia, with normal activation in the P pathway (Butler et al., 2001; Doniger et al., 2002; Foxe et al., 2001). One study used functional magnetic resonance imaging (fMRI) and reported hypoactivation of the M pathway (particularly in the right hemisphere) in persons with schizophrenia, but no evidence of abnormal functioning in the P pathway (Braus et al., 2002). There do not appear to be published studies specifically examining the magnitude of M pathway functioning using physiological methods in relatives of persons with schizo-phrenia, which would provide support for genetic contributions in M pathway dysfunction. We used fMRI (1.5 T) to examine M pathway functioning in 13 nonpsychotic first-degree relatives and 11 controls. The groups did not significantly differ on age, gender, or visual acuity. Cortical localization of the M pathway was assessed by targeting a specific region of cortex (V5/MT) well established as a primary center along the M pathway (e.g., Ahlfors et al., 1999). During scanning, participants viewed a display that projected nine concentric black rings on a green background. During the movement condition, rings were presented sequentially (5 Hz), creating the illusion of a single ring expanding or contracting for a block length of 21.6 s. This was followed by all nine rings appearing simultaneously and stationary for 21.6 s. Blocks alternated eight times over two separate fMRI scanning runs. A statistical contrast of fMRI signal strength in bilateral cortical region V5 during blocks of moving, relative to stationary, rings was conducted. V5 was defined bilaterally based on average location and variation from previous neuroimaging studies (e.g., Watson et al., 1993), using an initial 18-mm sphere centered on Talairach coordinates F 40, À 70, 3. A new sphere of …