Subcortical amygdala pathways enable rapid face processing

Human faces may signal relevant information and are therefore analysed rapidly and effectively by the brain. However, the precise mechanisms and pathways involved in rapid face processing are unclear. One view posits a role for a subcortical connection between early visual sensory regions and the amygdala, while an alternative account emphasises cortical mediation. To adjudicate between these functional architectures, we recorded magnetoencephalographic (MEG) evoked fields in human subjects to presentation of faces with varying emotional valence. Early brain activity was better explained by dynamic causal models containing a direct subcortical connection to the amygdala irrespective of emotional modulation. At longer latencies, models without a subcortical connection had comparable evidence. Hence, our results support the hypothesis that a subcortical pathway to the amygdala plays a role in rapid sensory processing of faces, in particular during early stimulus processing. This finding contributes to an understanding of the amygdala as a behavioural relevance detector.

Using high spatial resolution fMRI to understand representation in the auditory network

Following rapid methodological advances, ultra-high field (UHF) functional and anatomical magnetic resonance imaging (MRI) has been repeatedly and successfully used for the investigation of the human auditory system in recent years. Here, we review this work and argue that UHF MRI is uniquely suited to shed light on how sounds are represented throughout the network of auditory brain regions. That is, the provided gain in spatial resolution at UHF can be used to study the functional role of the small subcortical auditory processing stages and details of cortical processing. Further, by combining high spatial resolution with the versatility of MRI contrasts, UHF MRI has the potential to localize the primary auditory cortex in individual hemispheres. This is a prerequisite to study how sound representation in higher-level auditory cortex evolves from that in early (primary) auditory cortex. Finally, the access to independent signals across auditory cortical depths, as afforded by UHF, may reveal the computations that underlie the emergence of an abstract, categorical sound representation based on low-level acoustic feature processing. Efforts on these research topics are underway. Here we discuss promises as well as challenges that come with studying these research questions using UHF MRI, and provide a future outlook.

The involvement of monocular channels in the face pareidolia effect

Studies examining the neural mechanisms of face perception in humans have mainly focused on cortical networks of face-selective regions. However, subcortical regions are known to play a significant role in face perception as well. For instance, upon presenting pairs of faces sequentially to the same eye or to different eyes, superior performance is observed in the former condition. This superiority was explained by monocular, pre-striate processing of face stimuli. One of the intriguing face-related effects is the face pareidolia phenomenon, wherein observers perceive faces in inanimate objects. In this study, we examined whether face pareidolia involves similar low-level neural substrates to those that are involved in face perception. We presented participants with pairs of houses or face-like houses using a stereoscope to manipulate the information presented to each eye and asked them to determine whether the stimuli were similar or different. We managed to examine the contribution of monocular channels (mostly subcortical) in processing face-like stimuli. We hypothesized that besides their involvement in actual face perception, subcortical structures are engaged in face pareidolia as well. To test our hypothesis, we conducted three experiments to replicate and strengthen the reliability of our results and rule out alternative explanations. We demonstrated a perceptual benefit when presenting similar face-like houses to the same eye in comparison to their presentation to different eyes. This finding matches previous results found for images of real faces and indicates subcortical involvement not only in face perception but also in processing face-like objects.