Decoding and driving of brain activity, Gregor Thut and Marios Philiastides
This symposium aims at a broad audience interested in the significance of rhythmic brain activity for cognitive function. Two key aspects will be in the spotlight: 1) What do brain rhythms code for and how do they give rise to the complexity and efficiency in human behaviour? 2) How can we drive brain rhythms and establish their causal role in cognition through brain stimulation?
Brain stimulation as a tool to interact with brain oscillations: hits and misses
Domenica Veniero (University of Glasgow)
In recent years the investigation of brain oscillations has received increasing interest. Many studies have demonstrated that every cognitive process seems to be consistently associated to brain oscillations showing distinctive temporal, spatial and spectral signatures. But are these oscillations causally involved in cognition or are they a mere epiphenomenon? Non-invasive brain stimulation (NIBS) provides a possible way to directly address this question by allowing us to interact with brain oscillations. In my talk I will briefly review the basic principles of NIBS and then I will provide some successful examples of how we can apply brain stimulation to gain insight about the causal role of brain oscillations in shaping perception and in orchestrating neural network involved in different cognitive tasks. However, I will also point out the limitations we face when we try to manipulate brain oscillations with NIBS and show some unsuccessful attempt to modulate posterior brain rhythms.
How a desynchronized cortex and a synchronized hippocampus cooperatively form and retrieve memories
Simon Hanslmayr (University of Birmingham)
Brain oscillations have been proposed to be one of the core mechanisms underlying episodic memory. But how do they operate in the service of memory? Reviewing the literature a conundrum emerges as some studies highlight the role of synchronized oscillatory activity, whereas others highlight the role of desynchronized activity. In this talk, I will describe a recently published computational model that resolves this conundrum and parsimoniously shows how these two opposing oscillatory behaviours may cooperate in the service of memory. Building on empirical evidence, I will argue that the synchronization and desynchronization reflect a division of labour between a hippocampal and a neocortical system, respectively. Specifically, whereas desynchronization is key for the neocortex to represent information, synchronization in the hippocampus is key to bind information. I will then derive specific predictions that arise from this model about how the interaction between a synchronized hippocampus and a desynchronized neocortex is supposed to look like. These predictions will be assessed in a number of empirical studies ranging from non-invasive EEG and MEG data, invasive and non-invasive brain stimulation studies, and studies using intracranial recordings in human epilepsy patients. Together, these data support the notion that a desynchronized neocortex together with a synchronized hippocampus implement memory encoding and retrieval operations in the human brain.
Rhythmic brain activity as a substrate for audiovisual temporal integration
Roberto Cecere (University of Glasgow)
Each object or event in the real world is characterised by a number of unique physical properties that can be captured by one or more of our senses. The human brain has the remarkable ability to extract these isolated sensory features and merge them in a coherent percept, which yields a more accurate description of the environment. One of the most important factors determining whether multisensory inputs are bound together is their temporal proximity. In my talk I will show that rhythmic brain activity (i.e. brain oscillations) mechanistically determines when and how auditory and visual information are combined in the brain. Using audio-visual illusions as a proxy for multisensory binding in combination with rhythmic brain stimulation, I will first demonstrate how the temporal window of audio-visual interactions causally depends on the frequency of posterior brain oscillations. Then, I will show how spontaneous, trial-by-trial fluctuations in the amplitude of these oscillations are instead predictive of how strong those stimuli falling within the temporal window are integrated and those falling outside are separated. These data provide evidence that different features of brain oscillations, namely frequency and amplitude, relate to different aspects of multisensory perception, namely the temporal window of integration and its sharpness.
Systematic non-stationarity of α-oscillations in the human brain: Long term frequency sliding and power changes
Christopher S.Y. Benwell (University of Glasgow)
An implicit assumption underlying current theories and the analysis techniques employed by many electro- & magnetoencephalographic (EEG/MEG) studies investigating neural oscillations is that, in the absence of experimental manipulation, the properties of a neural ‘oscillator’ measurable at the scalp remain approximately stationary over time. Here, across several EEG and MEG experiments, we show that these assumptions are false for one of the most prominent frequency bands, the alpha-band. Specifically, alpha power increases and instantaneous frequency decreases systematically over the course of a typical experimental session (~1-2 hours). Our results suggest the existence of two non-stationary endogenous processes inherent in alpha-band activity. Source-space analyses revealed that these processes may occur in partially overlapping cortical networks with a common right-lateralized focus along the ventral visual processing stream. As well as providing novel insight into the intrinsic properties of widespread neural networks, the findings are of fundamental importance for the analysis and interpretation of studies aimed at both identifying functionally relevant oscillatory networks, and also driving these networks through external entrainment.
Facilitation and inhibition in selective attention: Two sides of the same coin?
Heleen Slagter (University of Amsterdam)
Over the past few decades, much insight has been gained into how selective attention may filter information processing at the neural level, by directly boosting relevant information (target facilitation), and/or by suppressing irrelevant information (distractor inhibition). Yet, there is still debate as to how early these effects can occur and whether target facilitation and distractor inhibition are simply different sides of the same coin or whether they are controlled by distinct neural mechanisms. Moreover, recent work indicates that distractor suppression only emerges when information about the distractor can be derived directly from experience, suggesting that suppression of distracting information is expectation dependent. This also raises the question as to how attention and expectation interact to bias information processing. In my talk, I will discuss recent findings from several behavioral and EEG studies that examined how expectations about upcoming target or distractor locations and/or features influence facilitatory and inhibitory effects of attention on visual information processing and representation using ERPs, multivariate decoding analyses, and inverted encoding models. Collectively, these confirm an important role for alpha oscillatory activity in town-down biasing of attention to, and sharpening of representations of target locations. Yet, they also show that target facilitation and distractor suppression are differentially influenced by expectation, and rely at least in part on different neural mechanisms, with effects of distractor suppression selectively occurring after stimulus presentation. Moreover, in a study in which we orthogonally manipulated spatial attention and expectation, neither top-down factor influenced the first feedforward sweep of cortical information processing (before 100ms), despite clear modulations of pre-stimulus alpha-band activity. Collectively, these findings shed novel light on how attention and expectation interact to bias perception and indicate that target facilitation and distractor inhibition are subserved by distinct neural mechanisms.
Stimulus-driven brain rhythms and alpha entrainment: A cautionary note
Christian Keitel (University of Glasgow)
From the earliest days of recording the Human alpha rhythm, researchers have been fascinated with the possibility of driving alpha externally by means of visual flicker stimulation. This approach has since inspired diverse lines of research into the neural mechanisms underlying visual perception and its modulation by attention. However, it remains an open question whether stimulus-driven alpha is equivalent to the intrinsic rhythm. Data from a recent EEG study, measuring brain responses to strictly- and quasi-periodic visual stimuli, allows a critical discussion of whether the alpha rhythm can be externally driven, or entrained, through periodic visual stimulation and pits this notion against seemingly contradictory findings from frequency-tagging research (i.e. studying visual processing with flicker but assuming a superposition of stimulus-driven and intrinsic rhythms instead).
This symposium aims at a broad audience interested in the significance of rhythmic brain activity for cognitive function. Two key aspects will be in the spotlight: 1) What do brain rhythms code for and how do they give rise to the complexity and efficiency in human behaviour? 2) How can we drive brain rhythms and establish their causal role in cognition through brain stimulation?
Brain stimulation as a tool to interact with brain oscillations: hits and misses
Domenica Veniero (University of Glasgow)
In recent years the investigation of brain oscillations has received increasing interest. Many studies have demonstrated that every cognitive process seems to be consistently associated to brain oscillations showing distinctive temporal, spatial and spectral signatures. But are these oscillations causally involved in cognition or are they a mere epiphenomenon? Non-invasive brain stimulation (NIBS) provides a possible way to directly address this question by allowing us to interact with brain oscillations. In my talk I will briefly review the basic principles of NIBS and then I will provide some successful examples of how we can apply brain stimulation to gain insight about the causal role of brain oscillations in shaping perception and in orchestrating neural network involved in different cognitive tasks. However, I will also point out the limitations we face when we try to manipulate brain oscillations with NIBS and show some unsuccessful attempt to modulate posterior brain rhythms.
How a desynchronized cortex and a synchronized hippocampus cooperatively form and retrieve memories
Simon Hanslmayr (University of Birmingham)
Brain oscillations have been proposed to be one of the core mechanisms underlying episodic memory. But how do they operate in the service of memory? Reviewing the literature a conundrum emerges as some studies highlight the role of synchronized oscillatory activity, whereas others highlight the role of desynchronized activity. In this talk, I will describe a recently published computational model that resolves this conundrum and parsimoniously shows how these two opposing oscillatory behaviours may cooperate in the service of memory. Building on empirical evidence, I will argue that the synchronization and desynchronization reflect a division of labour between a hippocampal and a neocortical system, respectively. Specifically, whereas desynchronization is key for the neocortex to represent information, synchronization in the hippocampus is key to bind information. I will then derive specific predictions that arise from this model about how the interaction between a synchronized hippocampus and a desynchronized neocortex is supposed to look like. These predictions will be assessed in a number of empirical studies ranging from non-invasive EEG and MEG data, invasive and non-invasive brain stimulation studies, and studies using intracranial recordings in human epilepsy patients. Together, these data support the notion that a desynchronized neocortex together with a synchronized hippocampus implement memory encoding and retrieval operations in the human brain.
Rhythmic brain activity as a substrate for audiovisual temporal integration
Roberto Cecere (University of Glasgow)
Each object or event in the real world is characterised by a number of unique physical properties that can be captured by one or more of our senses. The human brain has the remarkable ability to extract these isolated sensory features and merge them in a coherent percept, which yields a more accurate description of the environment. One of the most important factors determining whether multisensory inputs are bound together is their temporal proximity. In my talk I will show that rhythmic brain activity (i.e. brain oscillations) mechanistically determines when and how auditory and visual information are combined in the brain. Using audio-visual illusions as a proxy for multisensory binding in combination with rhythmic brain stimulation, I will first demonstrate how the temporal window of audio-visual interactions causally depends on the frequency of posterior brain oscillations. Then, I will show how spontaneous, trial-by-trial fluctuations in the amplitude of these oscillations are instead predictive of how strong those stimuli falling within the temporal window are integrated and those falling outside are separated. These data provide evidence that different features of brain oscillations, namely frequency and amplitude, relate to different aspects of multisensory perception, namely the temporal window of integration and its sharpness.
Systematic non-stationarity of α-oscillations in the human brain: Long term frequency sliding and power changes
Christopher S.Y. Benwell (University of Glasgow)
An implicit assumption underlying current theories and the analysis techniques employed by many electro- & magnetoencephalographic (EEG/MEG) studies investigating neural oscillations is that, in the absence of experimental manipulation, the properties of a neural ‘oscillator’ measurable at the scalp remain approximately stationary over time. Here, across several EEG and MEG experiments, we show that these assumptions are false for one of the most prominent frequency bands, the alpha-band. Specifically, alpha power increases and instantaneous frequency decreases systematically over the course of a typical experimental session (~1-2 hours). Our results suggest the existence of two non-stationary endogenous processes inherent in alpha-band activity. Source-space analyses revealed that these processes may occur in partially overlapping cortical networks with a common right-lateralized focus along the ventral visual processing stream. As well as providing novel insight into the intrinsic properties of widespread neural networks, the findings are of fundamental importance for the analysis and interpretation of studies aimed at both identifying functionally relevant oscillatory networks, and also driving these networks through external entrainment.
Facilitation and inhibition in selective attention: Two sides of the same coin?
Heleen Slagter (University of Amsterdam)
Over the past few decades, much insight has been gained into how selective attention may filter information processing at the neural level, by directly boosting relevant information (target facilitation), and/or by suppressing irrelevant information (distractor inhibition). Yet, there is still debate as to how early these effects can occur and whether target facilitation and distractor inhibition are simply different sides of the same coin or whether they are controlled by distinct neural mechanisms. Moreover, recent work indicates that distractor suppression only emerges when information about the distractor can be derived directly from experience, suggesting that suppression of distracting information is expectation dependent. This also raises the question as to how attention and expectation interact to bias information processing. In my talk, I will discuss recent findings from several behavioral and EEG studies that examined how expectations about upcoming target or distractor locations and/or features influence facilitatory and inhibitory effects of attention on visual information processing and representation using ERPs, multivariate decoding analyses, and inverted encoding models. Collectively, these confirm an important role for alpha oscillatory activity in town-down biasing of attention to, and sharpening of representations of target locations. Yet, they also show that target facilitation and distractor suppression are differentially influenced by expectation, and rely at least in part on different neural mechanisms, with effects of distractor suppression selectively occurring after stimulus presentation. Moreover, in a study in which we orthogonally manipulated spatial attention and expectation, neither top-down factor influenced the first feedforward sweep of cortical information processing (before 100ms), despite clear modulations of pre-stimulus alpha-band activity. Collectively, these findings shed novel light on how attention and expectation interact to bias perception and indicate that target facilitation and distractor inhibition are subserved by distinct neural mechanisms.
Stimulus-driven brain rhythms and alpha entrainment: A cautionary note
Christian Keitel (University of Glasgow)
From the earliest days of recording the Human alpha rhythm, researchers have been fascinated with the possibility of driving alpha externally by means of visual flicker stimulation. This approach has since inspired diverse lines of research into the neural mechanisms underlying visual perception and its modulation by attention. However, it remains an open question whether stimulus-driven alpha is equivalent to the intrinsic rhythm. Data from a recent EEG study, measuring brain responses to strictly- and quasi-periodic visual stimuli, allows a critical discussion of whether the alpha rhythm can be externally driven, or entrained, through periodic visual stimulation and pits this notion against seemingly contradictory findings from frequency-tagging research (i.e. studying visual processing with flicker but assuming a superposition of stimulus-driven and intrinsic rhythms instead).