How light that disrupts visible daily rhythms affects timing signals in two parts of the brain's biological clock

Constant light exposure seemingly abolished the c-Fos rhythm in the whole suprachiasmatic nucleus (SCN).

• The rhythm of c-Fos-immunoreactive cells persisted in the ventrolateral (vl) and dorsomedial (dm) parts of the SCN despite constant light.
• In the dm-SCN, the c-Fos rhythm was phase-delayed by about 4 hours under constant light.
• The PER1-immunoreactive rhythm was only slightly affected in the dm-SCN during constant light.
• In the vl-SCN, the c-Fos rhythm may be delayed by 5-6 hours compared to previously reported patterns.
• The rhythm of PER1 in the vl-SCN appeared out of phase with that observed in darkness.
• After a 9-hour light pulse, the PER1 rhythm in the vl-SCN was abolished, while the dm-SCN showed only slight changes.

Simplified