The emotion-action link? Naturalistic emotional stimuli preferentially activate the human dorsal visual stream.

A large body of brain imaging research highlights a set of specific regions in the limbic, insular and prefrontal cortex as sensitive to static visual images of high emotional content. Here we report that when using more naturalistic stimuli (short audio-visual video clips) the most selective cortical loci demonstrating preferential activation to emotional content were centered on the dorsal, action related, stream of visual areas. Subjects underwent fMRI scanning while watching a set of highly emotional as well as neutral video clips. Following the scan, clips were rated by each subject for emotional arousal and valence. Surprisingly, activity in dorsal stream visual areas (such as IPS and SPL) showed the highest preference to emotional arousal compared to all other brain areas. In contrast, ventral stream visual areas showed a significantly weaker emotional preference. Control experiments ruled out low level visual or auditory cues as contributing factors to this effect. Furthermore, the specific spatial pattern of emotion-related activations was incompatible with general arousal or attentional effects. Given the established role of dorsal stream visual areas in action-related functions, these results support the long held hypothesis associating emotion with preparation for action.

The day-after effect: long term, Hebbian-like restructuring of resting-state fMRI patterns induced by a single epoch of cortical activation.

During rest, the cerebral cortex displays rich, coordinated patterns of spontaneous activity. The mechanism that shapes these patterns is largely unknown. Here we demonstrate that a Hebbian-like, sustained process plays a role in focusing these coherent patterns. Human subjects used an fMRI-based neurofeedback (NF) paradigm to intensely activate the dorsal anterior cingulate cortex for a single epoch (30 min). Resting-state correlations between all of the cortical voxels' BOLD time courses (functional connectivity) were mapped before, immediately after, and one day after the NF session. We found that the single epoch of cortical activation induced a lasting restructuring of the functional connections according to a Hebbian-like rule. Therefore, the change (increase and decrease) in functional connectivity strength of cortical voxels during rest reflected the level of their prior coactivation during the NF epoch. Interestingly, the effect was significantly enhanced 1 d after the NF activation epoch. The effect was evident in each subject individually, indicating its potential as a diagnostic window into the personal history of prior brain activations of both healthy and abnormal individuals.

Give it time: neural evidence for distorted time perception and enhanced memory encoding in emotional situations.

Time perception is compromised in emotional situations, yet our ability to remember these events is enhanced. Here we suggest how the two phenomena might be functionally linked and describe the neural networks that underlie this association. We found that participants perceived an emotionally aversive stimulus longer than it was, compared to an immediately following neutral stimulus. These time estimation errors were in the same trials associated with better recognition memory for the emotionally aversive stimuli and poorer memory for the neutral stimuli. Functional imaging revealed that the superior frontal gyrus was activated during time perception with aversive stimuli, and the amygdala, putamen and insula showed activations that are specific to time estimation errors in this aversive context. We further found that activity in the insula and putamen was correlated with memory performance but only during over-estimation of time with the aversive stimuli. We suggest that processing is accelerated during the experience of emotionally aversive events, presumably in the service of memory-related operations, resulting in better encoding but at the expense of time perception accuracy.

Transformative art: art as means for long-term neurocognitive change.

Every artwork leads to a unique experience by the observer or participant, may it be sensory, emotional, cognitive, interactive, or spiritual experience. At the neurobiological level, such experiences are manifested as activation of the corresponding neural networks. Neuroscience has demonstrated that experience, in particular repeated experience, can cause a long-term change in the involved brain circuits (experience-dependent plasticity). This review will discuss the molding and transformative aspect of arts, examining how repeated and on-going experience of arts may alter cognitive, emotional, and behavioral patterns as well as their underlying neural circuits. The application of this approach to cognitive training and neuropsychological rehabilitation methods will be addressed as well. In addition, it will be suggested that this approach to art, as a long-term transformative medium, may lead to a novel viewpoint on art and a different approach to its creation. Artists can design artworks that aspire to form, in addition to one-shot influencing experience, on-going experiences which gradually create a lasting change, possibly improving audiences' neuropsychological functions.

Stimulus-free thoughts induce differential activation in the human default network.

Despite extensive research of the Default network, a set of regions which tend to reduce their activity relative to rest in response to stimulus-driven tasks, its function is still debated. Specifically, it is still not clear to what extent the activation profile of this network is driven by processes related to external stimulation (inhibitory or anticipatory), or is driven by specific thought contents. To address this question, we examined the ability of thoughts, generated in the absence of external stimulation, to modulate default network activation. In a set of experiments, several types of long lasting stimulus-free thoughts were elicited by brief (<1s) auditory cues. Sustained (40s) brain activations, far outlasting the cue, were demonstrated during these stimulus-free conditions. Importantly, brain activity in the default network showed a striking modulation associated with stimulus-free thought content. More specifically, a preferential activation was observed in essentially the entire default network during volitional-prospection thoughts when compared to the other stimulus-free thought conditions. Furthermore, several regions of the default network showed long-lasting above rest activations during the volitional-prospection condition. Our results demonstrate that default network activation can be modulated in the absence of external stimuli, thus pointing to the importance of thought-content in default-network specialization. Furthermore, together with previous research, these results support the notion that intrinsically oriented processing is a core specialization of the default network. Finally, our stimulus-free experimental paradigm introduces a new method for studying default network functionality.

Mapping dynamic memories of gradually changing objects.

Our brain is able to maintain a continuously updated memory representation of objects despite changes in their appearance over time (aging faces or objects, growing trees, etc.). Although this ability is crucial for cognition and behavior, it was barely explored. Here, we investigate this memory characteristic using a protocol emulating face transformation. Observers were presented with a sequence of faces that gradually transformed over many days, from a known face (source) to a new face (target), in presentations separated by other stimuli. This practice resulted in a drastic change in the memory and recognition of the faces. Although identification of the source and older face instances was reduced, recent face instances were increasingly identified as the source and rated as highly similar to the memory of the source. Using an object perturbation method, we estimated the corresponding memory shift, showing that memory patterns shifted from the source neighborhood toward the target. Our findings suggest that memory is updated to account for object changes over time while still keeping associations with past appearances. These experimental results are broadly compatible with a recently developed model of associative memory that assumes attractor dynamics with a learning rule facilitated by novelty, shown to hold when objects change gradually over short timescales.

The effects of perceptual history on memory of visual objects.

We investigated how the recognition and perception of memory-stored visual objects are influenced by cumulative experience with similar stimuli. The memory of a face was established by training observers to identify a set of faces as either "friends" or "non-friends". Subsequently, for multiple daily sessions, observers continued to perform this identification task, in which presented faces included a sequence of morphed faces, gradually transforming from a friend face (source) to another initially distinguishable non-friend face (target), interleaved with other faces. Initially observers identified only the first part of the morph sequence as "friends". In experimental conditions for which the initial "friends" portion was at least 54% of the sequence, this portion increased along repeated daily practice, until eventually most of the sequence was identified as "friends". After this practice, perceived similarity between source and target faces was much higher than the average similarity between the other face images. These effects did not occur when the morph images were shown in random order using a similar protocol. In addition, corresponding recognition confusions between source and target faces were found. Our findings suggest that memories of objects can be changed as a result of exposure to similar stimuli and show the dependency of these changes on the order in which stimuli are presented and on their level of similarity.

Dynamics of memory representations in networks with novelty-facilitated synaptic plasticity.

The ability to associate some stimuli while differentiating between others is an essential characteristic of biological memory. Theoretical models identify memories as attractors of neural network activity, with learning based on Hebb-like synaptic modifications. Our analysis shows that when network inputs are correlated, this mechanism results in overassociations, even up to several memories "merging" into one. To counteract this tendency, we introduce a learning mechanism that involves novelty-facilitated modifications, accentuating synaptic changes proportionally to the difference between network input and stored memories. This mechanism introduces a dependency of synaptic modifications on previously acquired memories, enabling a wide spectrum of memory associations, ranging from absolute discrimination to complete merging. The model predicts that memory representations should be sensitive to learning order, consistent with recent psychophysical studies of face recognition and electrophysiological experiments on hippocampal place cells. The proposed mechanism is compatible with a recent biological model of novelty-facilitated learning in hippocampal circuitry.