Department of Psychology and the Neuroscience Research Centre, University of Otago, Dunedin, New Zealand.
Hippocampus. 2011 Oct;21(10):1074-81. doi: 10.1002/hipo.20821. Epub 2010 Jun 2.
Previous studies have shown only modest effects of supramammillary nucleus (SuM) dysfunction on theta frequency and learning in the water maze (WM), with larger effects in other tasks. However, theta recorded from SuM, and used to trigger the production of theta-like oscillations in the hippocampus, produced reversal of the deficit in WM learning produced by theta blocking. We explored this apparent inconsistency by analyzing the relationship between SuM and hippocampal theta in the control group of this theta-blocking experiment using coherence, phase analysis, and the directed transfer function. We found little evidence of an influence of SuM on the hippocampus in the bulk of WM learning-with some possibility of SuM becoming involved briefly later in learning. A learning-related increase in coherence was observed in conjunction with gradual phase reorganization of hippocampal theta in relation to SuM theta. This change in phase dynamics between the two structures was also correlated with a relative increase of the estimated direction of theta propagation from the SuM to the hippocampus. These results are consistent with the previous weak effects of SuM lesions and suggest that the use of SuM as a source to trigger hippocampal theta and recover function is likely to be due to coherence between SuM and some other structure that normally controls hippocampal theta during WM learning.
先前的研究表明，乳头上核（SuM）功能障碍对水迷宫（WM）中的θ频率和学习的影响仅适度，而在其他任务中的影响更大。然而，从 SuM 记录的并用于触发海马中类似θ振荡产生的θ波，可逆转θ阻断引起的 WM 学习缺陷。我们通过分析使用相干性、相位分析和有向传递函数对该θ阻断实验的对照组中的 SuM 和海马θ之间的关系，来探讨这种明显的不一致性。我们发现，在 WM 学习的大部分时间里，SuM 对海马的影响很小-在学习的后期，SuM 可能会短暂地参与其中。在与 SuMθ相关的海马θ的逐渐相位重新组织的同时，观察到与学习相关的相干性增加。这两个结构之间的相位动力学变化也与从 SuM 到海马的θ传播的估计方向的相对增加相关。这些结果与先前的 SuM 损伤的微弱影响一致，并表明使用 SuM 作为触发海马θ并恢复功能的源很可能是由于 SuM 与在 WM 学习过程中通常控制海马θ的其他结构之间的相干性所致。
