Common functional localizers to enhance NHP & cross-species neuroscience imaging research

Abstract

Functional localizers are invaluable as they can help define regions of interest, provide cross-study comparisons, and most importantly, allow for the aggregation and meta-analyses of data across studies and laboratories. To achieve these goals within the non-human primate (NHP) imaging community, there is a pressing need for the use of standardized and validated localizers that can be readily implemented across different groups. The goal of this paper is to provide an overview of the value of localizer protocols to imaging research and we describe a number of commonly used or novel localizers within NHPs, and keys to implement them across studies. As has been shown with the aggregation of resting-state imaging data in the original PRIME-DE submissions, we believe that the field is ready to apply the same initiative for task-based functional localizers in NHP imaging. By coming together to collect large datasets across research group, implementing the same functional localizers, and sharing the localizers and data via PRIME-DE, it is now possible to fully test their robustness, selectivity and specificity. To do this, we reviewed a number of common localizers and we created a repository of well-established localizer that are easily accessible and implemented through the PRIME-RE platform.

Keywords: Brain; Face; Localizers; Metadata; Non-human primate; Retinotopy; fMRI.

Fig. 1.

Phase-encoded visual retinotopic mapping rely on expanding/contracting annuli (left panels), clockwise/counterclockwise rotating wedges (middle panels). Stimuli (from Zhu and Vanduffel, 2019) can be flickering checkerboards or mixtures between flickering checkerboards and incorporated natural moving objects such as dynamic faces and walking subjects (left and middle panels). Such mapping results in a polar angle and eccentricity information from all voxels and a precise description of the retinotopic organization of the visual cortex (right panel; adapted from Vanduffel et al., 2014).

Fig. 2.

The conjunction of multiple localizers allows to identify interindividual variations in cortical functional organization. (A) Projection of the (visual and tactile) and (visual, tactile and auditory) conjunction onto the left and right flattened intraparietal cortex of two monkeys M1 and M2. Limits of intraparietal areas LOP, LIPv, LIPd, VIPm, VIPl and AIP defined based on the F6 Caret atlas. Adapted from Guipponi et al., 2013). (B) Anterior and medial cingulate face fields defined by local maxima for reward, blink, saccade and tactile to the face and to the shoulder localizers. Adapted from Cléry et al., 2018.

Fig. 3.

A) Number of blocks for estimating the location of the face patches. Subject participated in multiple sessions, with multiple runs per session, of a block design experiment (intact faces versus phase scrambled faces; data from Russ and Leopold, 2015). T-values were calculated for an increasing number of blocks within predefined face selective regions (14) and visually responsive regions (10). Mean and standard deviation of the calculated t-value for each set of blocks is displayed. A representative t-map for 4 sets of blocks are shown above. B) Mapping of face selectivity: comparison across research centers and tasks. NHP 1–5 were collected animals on the 4.7T Bruker Vertical bore at the National Institutes of Health. Three face-processing localizers were used, a Face/Objects (NHPs 1 and 2), Face/Scrambled images (NHP 3 and 4), and Face Regressor in a movie (NHP 5) (data from: Russ and Leopold 2015; Koyano et al., 2021; McMahon et al., 2015). In addition, the probabilistic face-selectivity maps from Janssens and colleagues (2014) is mapped to show the overlap between single subjects and the maps generated from separate subjects collected at 3T.

Fig. 4.

Monkey Kingdom: Four snapshots of the movie localizer “Monkey Kingdom”, released by Disney. The movie contains images of monkeys, humans, actions, social behavior, man-made and natural objects and scenes. The movie is entertaining for humans and attracts attention of monkeys and is currently used in several human and non-human imaging laboratories for cross-species homology research. For details see Box 2 and wim.vanduffel@kuleuven.be.

Fig. 5.

Contralateral modulation of visually-driven activity by covert selective spatial attention. Flattened and inflated cortical representations of the left and right hemispheres showing contralateral modulation of fMRI activity induced by covert attention to either the right (left panels) or to the left (right panels) while monkeys fixate to a central fixation spot. Areal boundaries are indicated by white outlines. T-score maps are shown in hot colors (right versus left attention for the left hemisphere and vice versa for the right hemisphere). The cortical representations of the stimuli are shown in green, and were obtained in independent sessions, without directed attention to the stimuli. Figure adapted from Caspari et al., 2015, where also the experimental details are described.