Production and characterization of neglect in rats with unilateral lesions of ventrolateral orbital cortex

Abstract

Neglect is a clinical syndrome characterized by an inability to orient, report, or respond to novel or meaningful stimuli presented to one side of the body or in one hemispace. Neglect in humans and monkeys most often results from damage to one of several interconnected cortical areas, including limbic cortex. In rats damage to only one cortical area, medial agranular cortex (AGm), has been found to produce neglect. Thus, it remains to be determined if there is a cortical circuitry related to neglect in rodents. AGm has extensive bilateral reciprocal connections with the paralimbic area ventrolateral orbital cortex (VLO). The current study was conducted to determine if lesions of VLO also result in neglect in the rat. Male Long-Evans hooded rats with lesions of right VLO (n = 7), left VLO (n = 7), and sham operates (n = 23) were tested for a minimum of 4 weeks on the following: (i) motor asymmetry based on assessment of rotational behavior during a 2-minute period, (ii) neglect based on the degree of orientation to visual, tactile, and auditory stimuli presented in each hemispace, and (iii) tactile extinction based on the tendency to touch the ipsilesional tab first when adhesive tabs were attached to each wrist. Lesions of VLO resulted in no obvious motor asymmetry. Both right and left VLO operates showed significant overall contralesional neglect relative to shams. However, whereas left VLO operates showed significant contralesional neglect relative to shams in the auditory and visual modalities, right VLO operates showed significant neglect in the tactile modality. On the extinction measure only right VLO operates demonstrated an asymmetry, left VLO operates were unimpaired.