After electrolytic lesions to the cortical and adjacent amygdaloid subnuclei, thresholds for rewarding medial forebrain bundle (MFB) stimulation were tracked in 19 rats with bilateral implants and 8 with single implants. Results were categorized into 3 groups depending on the magnitude of the lesion effect on ipsilateral frequency thresholds: substantial (> 60%), small (> 26%), or none (< 26%), compared with baseline values. Five rats exhibited threshold increases up to 225%, among the largest reported to the authors' knowledge. Small shifts were observed in another 5 rats, and no change in the remaining 17 rats. Threshold changes in the contralateral electrode mirrored ipsilateral ones. Results suggest that specific amygdaloid subnuclei modulate MFB reward signals through a diffuse collateralized organization of fibers and lend support to the existence of interhemispheric links in MFB reward pathways.