A Dwarakanath

Nonmonotonic spatial structure of interneuronal correlations in prefrontal microcircuits

Significance The spatial structure of correlated activity of neurons in lower-order visual areas has been shown to linearly decrease as a measure of distance. The shape of correlated variability is a defining feature of cortical microcircuits, as it constrains the computational power and diversity of a region. We show here a nonmonotonic spatial structure of functional connectivity in the prefrontal cortex (PFC) where distal interactions are just as strong as proximal interactions during visual engagement of functionally similar PFC neurons. Such a nonmonotonic structure of functional connectivity could have far-reaching consequences in rethinking the nature and role of prefrontal microcircuits in various cognitive states. Correlated fluctuations of single neuron discharges, on a mesoscopic scale, decrease as a function of lateral distance in early sensory cortices, reflecting a rapid spatial decay of lateral connection probability and excitation. However, spatial periodicities in horizontal connectivity and associational input as well as an enhanced probability of lateral excitatory connections in the association cortex could theoretically result in nonmonotonic correlation structures. Here, we show such a spatially nonmonotonic correlation structure, characterized by significantly positive long-range correlations, in the inferior convexity of the macaque prefrontal cortex. This functional connectivity kernel was more pronounced during wakefulness than anesthesia and could be largely attributed to the spatial pattern of correlated variability between functionally similar neurons during structured visual stimulation. These results suggest that the spatial decay of lateral functional connectivity is not a common organizational principle of neocortical microcircuits. A nonmonotonic correlation structure could reflect a critical topological feature of prefrontal microcircuits, facilitating their role in integrative processes.

Testing the perceptual equivalence hypothesis in mental rotation of 3D stimuli with visual and tactile input

Previous studies on mental rotation (i.e., the ability to imagine objects undergoing rotation; MR) have mainly focused on visual input, with comparatively less information about tactile input. In this study, we examined whether the processes subtending MR of 3D stimuli with both input modalities are perceptually equivalent (i.e., when learning within-modalities is equal to transfers-of-learning between modalities). We compared participants’ performances in two consecutive task sessions either in no-switch conditions (Visual→Visual or Tactile→Tactile) or in switch conditions (Visual→Tactile or Tactile→Visual). Across both task sessions, we observed MR response differences with visual and tactile inputs, as well as difficult transfer-of-learning. In no-switch conditions, participants showed significant improvements on all dependent measures. In switch conditions, however, we only observed significant improvements in response speeds with tactile input (RTs, intercepts, slopes: Visual→Tactile) and close to significant improvement in response accuracy with visual input (Tactile→Visual). Model fit analyses (of the rotation angle effect on RTs) also suggested different specification in learning with tactile and visual input. In “Session 1”, the RTs fitted similarly well to the rotation angles, for both types of perceptual responses. However, in “Session 2”, trend lines in the fitting analyses changed in a stark way, in the switch and tactile no-switch conditions. These results suggest that MR with 3D objects is not necessarily a perceptually equivalent process. Specialization (and priming) in the exploration strategies (i.e., speed-accuracy trade-offs) might, however, be the main factor at play in these results—and not MR differences in and of themselves.

Non-monotonic spatial structure of interneuronal correlations in prefrontal microcircuits

Correlated fluctuations of single neuron discharges, on a mesoscopic scale, decrease as a function of lateral distance in early sensory cortices, reflecting a rapid spatial decay of lateral connection probability and excitation. However, spatial periodicities in horizontal connectivity and associational input as well as an enhanced probability of lateral excitatory connections in the association cortex could theoretically result in non-monotonic correlation structures. Here we show such a spatially non-monotonic correlation structure, characterized by significantly positive long-range correlations, in the inferior convexity of the macaque prefrontal cortex. This functional connectivity kernel was more pronounced during wakefulness than anesthesia and could be largely attributed to the spatial pattern of correlated variability between functionally similar neurons during structured visual stimulation. These results suggest that the spatial decay of lateral functional connectivity is not a common organizational principle of neocortical microcircuits. A non-monotonic correlation structure could reflect a critical topological feature of prefrontal microcircuits, facilitating their role in integrative processes. Significance statement The spatial structure of correlated activity of neurons in lower-order visual areas has been shown to linearly decrease as a measure of distance. The shape of correlated variability is a defining feature of cortical microcircuits as it constrains the computational power and diversity of a region. We show here for the first time a non-monotonic spatial structure of functional connectivity in the pre-frontal cortex where distal interactions are just as strong as proximal interactions during visual engagement of functionally similar PFC neurons. Such a nonmonotonic structure of functional connectivity could have far-reaching consequences in rethinking the nature and the role of prefrontal microcircuits in various cognitive states.

The Role of the Occipital Cortex in Resolving Perceptual Ambiguity

During observation of an ambiguous stimulus, our perception alternates spontaneously between mutually exclusive interpretations, although the physical stimulus remains constant. Although the term “ambiguous stimulus” often evokes thoughts of a single image that can be interpreted in two ways (e.