Symposia abstracts > Monday 23rd October 9.45am-11am

Interrelations between the Representation of Time and Space (Martin Riemer)

Speakers: Martin Riemer (Germany), Roberto Bottini (Italy), Baptiste Gauthier (France), Filomena Anelli (Italy)

The concepts of space and time are highly intertwined in the human mind. We all are familiar with graphical illustrations of temporal sequences, in which successive events are ordered next to each other along a spatial continuum. The localization of events in time (before/after) and the magnitude of durations (short/long) are often coded with a left-to-right spatial order on a ‘mental time line’ (Bonato, Zorzi, & Umilta, 2012). Linguistic approaches point out that we often use spatial metaphors to describe relations in time. The future lies in front of us and past events might be far away. Spatial metaphors for time are accompanied by body gestures, e.g., pointing backwards to indicate that something happened in the past. All these examples demonstrate the general tendency of the human mind to conceptualize in space what is perceived in time (Casasanto & Boroditsky, 2008).

In support of this view, neuroimaging studies have discovered neural populations in the parietal cortex that code both for temporal and spatial magnitudes, and damages in these areas can impair time perception as well as spatial cognition. More recently, the discovery of place and grid cells in the hippocampus and the entorhinal cortex, and the observation that these cells exhibit spatial and temporal tuning curves provide new insights to the neuronal substrates of interrelations between time and space (Kraus et al., 2015).  Yet, this wealth of empirical observations is still lacking a coherent theoretical framework that could explain (i) universal and culture-specific aspects of space-time interactions, (ii) whether the cognitive systems for time and space interact in a symmetric or an asymmetric manner, (iii) and whether different forms of space-time interactions (from magnitude judgments to mental time travel) can be traced back to one core neural system or are based on largely different mechanisms.

In our symposium, we will present and discuss the results from recent fMRI and MEG/EEG studies, directly comparing neuroanatomical contributions to time and space representations in healthy participants (Riemer). As vision is a pertinent factor for the formation and maintenance of spatial representations, the impact of visual experience of space for time-space interactions will be addressed by comparing sighted and visually impaired participants (Bottini).  Interrelations between time and space are not confined to direct perception. They also affect our ability to imagine and mentally represent these dimensions. The second part of our symposium will therefore focus on the question of how mental travel through time is influenced by spatial factors and vice versa. Again, we will discuss the ability for mental travel through time and space in healthy participants (Gauthier) and in brain-damaged neglect patients with a deficit in spatial attention (Anelli).

Evaluation of competing hypotheses can produce a common working framework to investigate the links between time and space that are fundamental aspects of human cognition. 

 

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Neural Entrainment as a Mechanism of Efficient Stimulus Processing (Benedikt Zoefel)

Speakers: Monica N. O’Connell (USA), Molly J. Henry (Canada), Sanne Ten Oever (The Netherlands), Benedikt Zoefel (UK)

Neural entrainment, the alignment between neural oscillations and rhythmic stimulus input, is often assigned a critical role for stimulus processing, selection, and predictions: By aligning the high-excitability oscillatory phase with the timing of expected events, important stimulus input can be selectively amplified (e.g., Schroeder & Lakatos, 2009). Nevertheless, studies are often criticized, due to an apparent failure to distinguish neural entrainment from other processes that can potentially produce similar data, or due to a lack of understanding of the underlying neural mechanisms.

In this symposium, we use state-of-the-art methods to address these issues in several studies. In the first talk (MN O’Connell), we demonstrate in intracranial non-human primate recordings that a network comprising non-specific thalamic and cortical regions is critically involved in the phase-reset of neural oscillations, a fundamental mechanism for an efficient adjustment to stimulus input and an often hypothesized process underlying neural entrainment (e.g., Lakatos et al., 2009). In two subsequent talks, we show that neural entrainment is not merely a superposition of regular evoked responses, an issue raised previously (e.g., Capilla et al., 2011): In electroencephalographic (EEG) data (MJ Henry), we show that neural entrainment can be dissociated from evoked responses by independently manipulating the perceived beat and acoustic properties of a rhythmic musical stimulus. In magnetoencephalographic (MEG) recordings (S Ten Oever), we show that neural entrainment persists when participants do not consciously perceive the entraining stimulus (which strongly reduces evoked neural activity).  In the last talk of the symposium (B Zoefel), we use combined transcranial alternating current stimulation (tACS) and functional magnetic resonance imaging (fMRI) recordings to demonstrate that neural entrainment is not only an epi-phenomenon but causally involved in speech processing: Manipulating the phase relation between neural oscillations and speech rhythm affects the blood-oxygen-level dependent (BOLD) response to intelligible (but not unintelligible) speech.

Together, our symposium provides important and complementary evidence that neural entrainment is more than a simple repetition of evoked responses: Instead, it reflects an efficient mechanism for the processing of rhythmic stimulus input, including speech sounds, and involving thalamocortical connections as one of the underlying neural circuitries. 

 

 
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