King A J, Schnupp J W, Carlile S, Smith A L, Thompson I D
University Laboratory of Physiology, Oxford, UK.
Prog Brain Res. 1996;112:335-50. doi: 10.1016/s0079-6123(08)63340-3.
The role of the superior colliculus in attending and orienting to sensory stimuli is facilitated by the presence within this midbrain nucleus of superimposed maps of different sensory modalities. We have studied the steps involved in the development of topographically-aligned maps of visual and auditory space in the ferret superior colliculus. Injections of fluorescent beads into the superficial layers showed that the projection from the contralateral retina displays topographic order on the day of birth (PO). Recordings made from these layers at the time of eye opening, approximately 1 month later, revealed the presence of an adult-like map of visual space. In contrast, the auditory space map in the deeper layers emerged gradually over a much longer period of postnatal life. In adult ferrets in which one eye had been deviated laterally just before eye opening, the auditory spatial tuning of single units recorded in the contralateral superior colliculus was shifted by a corresponding amount, so that the registration of the visual and auditory maps was maintained. Chronic application of the NMDA-receptor antagonist MK801 disrupted the normal development of the auditory space map, but had no effect on the visual map in either juvenile or adult animals, or on the auditory map once it had matured. These findings indicate that visual cues may play an instructive role, possibly via a Hebbian mechanism of synaptic plasticity, in the development of appropriately tuned auditory responses, thereby ensuring that the neural representations of both modalities share the same coordinates. Changes observed in the auditory representation following partial lesions of the superficial layers at PO suggest that these layers may provide the source of the visual signals responsible for experience-induced plasticity in auditory spatial tuning.
上丘在参与和定向感觉刺激方面的作用，因该中脑核内存在不同感觉模态的叠加图谱而得到促进。我们研究了雪貂上丘中视觉和听觉空间的地形对齐图谱发育过程中的各个步骤。向表层注射荧光珠显示，出生当天（PO），来自对侧视网膜的投射呈现出地形顺序。大约1个月后，在睁眼时从这些层进行的记录揭示了视觉空间的成人样图谱的存在。相比之下，深层的听觉空间图谱在出生后的更长时期内逐渐形成。在成年雪貂中，其中一只眼睛在睁眼前不久向外侧偏斜，对侧上丘中记录的单个神经元的听觉空间调谐相应地发生了偏移，从而保持了视觉和听觉图谱的对齐。长期应用NMDA受体拮抗剂MK801会破坏听觉空间图谱的正常发育，但对幼年或成年动物的视觉图谱或成熟后的听觉图谱均无影响。这些发现表明，视觉线索可能通过突触可塑性的赫布机制，在适当调谐的听觉反应的发育中发挥指导作用，从而确保两种模态的神经表征共享相同的坐标。出生当天对上丘表层进行部分损伤后，在听觉表征中观察到的变化表明，这些层可能提供了负责听觉空间调谐中经验诱导可塑性的视觉信号来源。
