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Vision Lab Talk Series Present:


Peter Tse
Dartmouth College
Friday, June 10
12:00 - 1:20 pm
WJH room 601

Historical Background: The artifact record suggests that the minds of earlier species in our genus were singularly unimaginative. For example, the Acheulian handaxes of Homo Erectus hardly changed over more than a million years. Even the more sophisticated Mousterian technology of the Neanderthals was stable over many tens of thousands of years.

With the advent of our species, however, innovation in art and technology became explosive. What changed in our brains to permit our species to become so innovative and creative? I will begin with some ideas in this regard, before getting into the details of fMRI data from three experiments on mental operations over imagined objects.

In particular, I will argue that changes in the circuitry commonly thought to underlie volitional manipulation of operands in working memory was central to the development of our species' creativity. Scientific Background: In Baddeley’s (1986) model of working memory, the brain manipulates mental representations via a central executive system that directs activity in subsystems like the visuospatial sketchpad. Many neuroimaging studies implicate a network including the dorsolateral prefrontal cortex (DLPFC) and posterior parietal cortex (PPC) as the neural correlate of this model (e.g. Schlegel, et al., 2013). Current understanding suggests that DLPFC acts as Baddeley’s central executive, directing transformations of mental representations in other regions rather than storing representations directly. For instance, Crowe and colleagues (2013) showed that neurons in monkey prefrontal cortex transmit executive control signals to parietal neurons.

Question: Most research has focused on representations (faces, objects, scenes etc.) which can be the operands of mental operations. Much less work has focused on the mental operations themselves, probably because these are trickier to study, at least with fMRI. To address this, and to examine the neural basis of mental operations over mental operands, we asked whether DLPFC, PPC and other areas direct the manipulation of mental imagery or if they are also involved in representing mental images themselves, or both. Method: We developed a hierarchy of abstract shapes and an orthogonal hierarchy of mental operations that could be performed on those shapes. In each of a series of trials, participants performed a particular mental operation on a particular shape. Mental operations included assembling, disassembling, and rotating visualized shapes. Results: Using multivariate pattern classification methods on neural activity in DLPFC, we could decode both the shape that participants imagined and the mental operation that they performed.

Representational similarity analyses showed that the informational structures of both DLPFC and PPC correlated significantly with both the shape and the operation hierarchies, although DLPFC correlated more with the operation hierarchy and PPC correlated more with the shape hierarchy. In certain core areas that likely subserve volitional mental operations, using such a correlational approach, we were able to decode the stages of mental operations as they unfolded over seconds. We also find that motor circuitry is integrated into the core as needed, and that mental operations over operands in the internal virtual reality of our imagination may be built upon the same operations that we would carry out motorically, when we act in the real world. For example, we can decode a mental rotation of an imagined shape using a classifier created over actual hand rotations.

Conclusion: Our results suggest that information about both mentally imaged shapes and mental operations over such operands is distributed throughout specialized nodes of the frontoparietal network rather than localized to particular regions. And we find that we may manipulate objects in the virtual reality of our imagination using the same operations that would govern our bodies in the real world. This suggests that Baddeley's hierarchical modularity is too simplistic and that volitional mental operations and mental operands are deeply integrated across core neural circuits subserving human imagination.