Despite the established role of the caudate nucleus in flexible behavior by linking actions and outcomes (Hikosaka et al., 2000; Yin et al., 2005; Graybiel, 2008; Balleine and O'Doherty, 2010), its role in the monitoring of such behavior is less clear.
First identified as a crystalline component of gallstones more than 200 years ago, cholesterol consists of a rigid, planar tetracyclic nucleus and a flexible, iso-octyl side-chain at carbon 17 (Nes, 2011).
Enucleated erythrocytes are more flexible and the lack of the nucleus creates more intracellular space for hemoglobin.
It is composed of two parts: a soft centre (nucleus pulposus) and a tough flexible ring (anulus fibrosus) around it.
Our findings that the caudate nucleus provides online monitoring of flexible behavior are consistent with a recent study showing that individual caudate neurons coded values of visual objects in a flexible manner (Kim and Hikosaka, 2013).
The endonuclear chromatin is continuously condensed and packaged during nuclear morphogenesis, making the nucleus not so rigid and somewhat flexible.
In parallel, the formation of hydrophobic nuclei and the consequent appearance of flexible polymer loops grafted to the semi-rigid cores is witnessed.
Comparison of the two patterns suggests that the conventional architecture prevails in eukaryotic nuclei because it results in more flexible chromosome arrangements, facilitating positional regulation of nuclear functions.
Therefore, our findings are complementary to the aforementioned study because we showed that the caudate nucleus provides abstract cognitive monitoring signals beyond flexible reward associations.
We should note that the TPPS4 monomers may also self-assemble into the two-dimensional flexible sheets with intrinsically chirality, and roll into the short nuclei of monolayered nanotube structures by the hydrodynamic effect44, 45.
In the nucleated conformational conversion (NCC) model, the flexible oligomers would experience structural rearrangement upon interaction with the nuclei, which eventually results in the amyloid fibril formation [54].
