MT neurons are highly selective for the direction of stimulus motion, and the area is believed to be a key component of the neural substrates of visual motion perception (for review, see Albright, 1993). If MT neurons have potential for associative plasticity similar to that seen in IT cortex, the behavioral pairing of motion directions with arrow

directions should lead to a convergence of responses to the paired stimuli, overtly detectable in MT as emergent responses to the arrows. Moreover, those responses should be tuned for arrow direction, and the form of that tuning should depend on the specific associations learned. Schlack and Albright (2007) tested these hypotheses by recording selleck products from MT neurons after the motion-arrow associations were learned. Many MT neurons exhibited selectivity for the direction of the static arrow—a property not seen prior to learning, and seemingly heretical to the accepted view that MT neurons are primarily selective for visual motion. Moreover, for individual neurons, the arrow-direction tuning curve was a close match buy OSI-744 to the motion-direction tuning curve (Figures 3C and 3D). To confirm that the emergent responses to arrows reflected the learned association with motions rather than specific physical attributes of the arrow stimulus, Schlack

and Albright (2007) trained a second monkey on the opposite associations (e.g., upward motion associated with downward arrow). As expected from the all learning hypothesis, the emergent tuning again reflected the association (e.g., if the preferred direction for motion was upward, the preferred direction

for the arrow was downward) rather than the specific properties of the associated stimulus. On the surface of things, the plasticity seen in area MT appears identical to that previously observed in IT cortex: the neuronal response change is learning-dependent and can be characterized as a convergence of responses to the paired stimuli. One might suppose, therefore, that the phenomenon in MT also reflects mechanisms for long-term memory storage. There are, however, several reasons to believe that the plasticity observed in MT reflects rather different functions and mechanisms. To begin with, IT and MT cortices are distinguished from one another by the availability of substrates for long-term memory storage. In the IT experiments described above the paired stimuli (arbitrary complex objects) are in all cases plausibly represented by separate groups of IT neurons, which means that connections between those representations could be forged locally within IT cortex. The same is not true for area MT, as there exists no native selectivity for stationary arrows (or for most other nonmoving stimuli). IT and MT are also distinguished from one another by the presence versus absence of feedback from cortical areas of the medial temporal lobe (see Figure 2).