Stimulus-specific adaptation detects sound novelty in macaque A1

The question of how the auditory system is able to automatically track unattended background sounds and detect novelty therein is one of the most intriguing ones in cognitive neuroscience. Electroencephalography and magnetoencephalography studies in humans have extensively documented associations between differential auditory cortex responses to sounds deviating from background stimulation (a.k.a. mismatch negativity responses) and the extent that these deviations in stimulation penetrate into the awareness of the subjects as reflected by disruptions of ongoing task performance. The underlying neural mechanisms have, however, been an issue of controversy, with a number of studies suggesting that stimulus-specific adaptation could serve as a relatively simple and ecological neurophysiological automatic sound deviance screening mechanism, and other studies arguing that there must be some other, more complex, mechanisms at play.

In their recent study, Fishman and Steinschneider (2012) studied carefully the underlying neural mechanisms by recording macaque primary auditory cortex responses to frequently repeating “standard” sounds and infrequently occurring “deviant” sounds in a conventional oddball paradigm and various control conditions. Taken together, their results suggest that stimulus-specific adaptation underlies detection of deviations in ongoing auditory stimulation  in the macaque primary auditory cortex. The authors caution that their recordings were confined within the macaque A1, and thus there could always be other mechanisms at play in secondary auditory cortical areas that should be investigated in future studies. These findings are highly significant in that they bridge the gap between human mismatch negativity research and animal models.  Indeed, it is fascinating to think that a relatively simple adaptation mechanism could underlie the relatively complex perceptual-cognitive level phenomena that the mismatch negativity response has been associated with, including auditory sensory memory and involuntary attention. 

Reference: Fishman YI, Steinschneider M. Searching for the mismatch negativity in primary auditory cortex of the awake monkey: deviance detection or stimulus specific adaptation? Journal of Neuroscience (2012) 32: 15747–15758. http://dx.doi.org/10.1523/JNEUROSCI.2835-12.2012

Dissociation between learning from one’s own mistakes and from errors made by others in Parkinson’s patients

In everyday life, one constantly faces situations where one has to make choices. These decisions are guided both by consequences, rewards and punishments, of one’s own choices in similar situations in the past, as well as by having observed others’ choices getting rewarded or punished. It has been, however, poorly known whether learning by observing others and learning from one’s own mistakes rely on the same vs. different underlying neural mechanisms. 

In Parkinson’s disease there is a bias to learn more from negative than positive feedback, which has been presumed to be due to loss of striatal dopaminergic function in the disease. It has not been, however, investigated whether there is a similar bias with respect to learning by observing successful and erroneous choices of others. Dissociation between these two types of learning in Parkison’s disease would suggest that dopaminergic system plays a differential role in trial-and-error vs. observational learning.

In their recent study, Kobza et al. (2012) investigated this highly interesting question in a total of 19 Parkinson’s patients and 40 healthy controls, divided into separate groups that were exposed to highly similar trial-and-error and observational learning tasks, respectively. The results showed that while Parkinson patients (who were off medication) exhibited a typical bias to learn better from negative than positive feedback when they were actively performing the task themselves, those Parkinson patients who learned by observation showed similar pattern of results as the healthy control subjects who learned better from positive than negative feedback. 

These findings indicate that there is a dissociation in the involvement of phasic dopamine activity in trial-and-error vs. observational learning. Dopaminergic activity, while clearly implicated when learning by getting positive and negative feedback based on one’s own active behavioral choices, would seem to be little involved in observational learning. These findings clearly justify further studies into the neural mechanisms underlying the ability to learn by observation.

Reference: Kobza S, Ferrea S, Schnitzler A, Pollok B, Südmeyer M, Bellebaum C Dissociation between active and observational learning from positive and negative feedback in Parkinsonism. PLoS ONE (2012) 7: e50250. http://dx.doi.org/10.1371/journal.pone.0050250

Recent studies shed light on how the brain processes temporally distributed information

The vast majority of cognitive neuroscience research has focused on mapping brain responses to static stimuli during highly simplified experimental paradigms, and indeed such studies have provided valuable information about the hierarchical processing steps that take place in the human brain, with sensory cortical areas processing relatively simple stimulus features and higher-order association cortical areas processing more complex aspects of perceptual objects. This is, however, only half of the story, as stimuli and events in the real world almost always take place in a temporal context. For example, the meaning of a single word is greatly shaped by the preceding words, gestures, and social interactions. Thus, the brain needs to have mechanisms that accumulate information over longer timescales in order to make sense of things that are unfolding across time.

Two distinct studies in the most recent issue of the prestigious journal Neuron have addressed the issue of where in the brain processing of temporally distributed information takes place using very interesting experimental setups. In the first study, Yaron et al. (2012) presented anesthetized rats with auditory stimulation that either contained periodicity or was completely random. The authors hypothesized that if auditory cortical neurons code periodicity information the responses to sounds presented in the periodicity-containing sequences should be smaller than responses to sounds when they are presented randomly. Indeed, their results showed this to be the case and the authors conclude that neurons in the auditory cortex are sensitive to the detailed structure of sound sequences over timescales even as long as minutes. In the second study, Honey et al. (2012) measured electrocorticography in human subjects during watching of intact and temporally scrambled movies. By inspecting the degree of synchrony of neuronal activity across cortical locations in the intact vs. scrambled movie conditions, the authors noted that while sensory cortical areas synchronized over very short times scales, within higher-order regions slow power fluctuations were more reliable for the intact than the scrambled movie, suggesting that these regions accumulate information over longer time periods.

These studies provide recent examples of a highly exciting and relatively new area of research that is focusing on how the brain is able to accumulate information over longer time scales to make sense of words, sentences, melodies, and patterns of social interactions. The finding that auditory cortex of rats can track periodicity over timescales of minutes is truly significant and is bound to inspire further research; on the other hand, the experimental setup of using scrambled vs. intact movies to investigate temporal receptive windows in humans based on recording of brain electrical activity provide a significant methodological step forward for further research in humans.

References:

Honey CJ, Thesen T, Donner TH, Silbert LJ, Carlson CE, Devinsky O, Doyle WK, Rubin N, Heeger DJ, Hasson U. Slow cortical dynamics and the accumulation of information over long timescales. Neuron (2012) 76: 423–434. http://dx.doi.org/10.1016/j.neuron.2012.08.011

Yaron A, Hershenhoren I, Nelken I. Sensitivity to complex statistical regularities in rat auditory cortex. Neuron (2012) 76: 603-615. http://dx.doi.org/10.1016/j.neuron.2012.08.025

Inferior frontal gyrus hemodynamic activity synchronizes between subjects engaging in face-to-face communication

Even though humans have evolved to communicate face-to-face, life in modern societies involves communication via email and phone to an increasingly large extent, and time spent on face-to-face communications is becoming less frequent. In contrast to these other forms of communication, face-to-face communication is characterized by rich audiovisual stimulation and non-verbal cues such as facial expressions and gestures that further provide cues for turn taking during conversations. It has been an open question, however, whether there are neurocognitive mechanisms that are specifically activated during face-to-face (and not during other forms of) interpersonal communication.

In their recent study, Jiang et al. (2012) recorded hemodynamic brain activity using near-infrared spectroscopy simultaneously from 10 pairs of interacting subjects to study whether there are brain responses that are elicited in synchrony in the interacting subjects' brains only during face-to-face communication. More specifically, their subjects engaged in face-to-face dialogue, face-to-face monologue, back-to-back dialogue, and back-to-back monologue while their brain hemodynamic activity was recorded. The authors observed synchronization of hemodynamic activity in the inferior frontal gyrus among the conversing subject pairs that was specific to face-to-face conversation. A further analysis of the dynamics of inferior frontal gyrus synchronization suggested that the activity was due to face-to-face interactions such as turn-taking behavior rather than mere verbal signal transmission.

These findings suggest that face-to-face communication involves interpersonal brain activity patterns that other types of communication lack. These novel findings are highly interesting also from the perspective that simultaneous recording of brain activity from two interacting subjects has become a very exciting area of research (that is often referred to as two-person neuroscience or hyperscanning), and Jiang et al. (2012) demonstrate in their study that the approach can indeed be utilized to capture neuroscientifically interesting phenomena that take place specifically during two-person interactions.

Reference: Jiang J, Dai B, Peng D, Zhu C, Liu L, Lu C. Neural synchronization during face-to-face communication. Journal of Neuroscience (2012) 32: 16064–16069. http://dx.doi.org/10.1523/JNEUROSCI.2926-12.2012

Flow proneness correlates with dorsal striatum dopamine D2 receptor binding potential

Being in a “flow state” refers to a state of enthusiasm with high but subjectively effortless attention, reduced sense of self-awareness, and control during challenging tasks that match in difficulty the competence level of a person. In many tasks such as competitive sports and work, flow state is often sought to improve performance. The neural basis of the phenomenon of flow has been a topic of speculation, however, there are lines of research suggesting links between dopamine system and flow state, for example, higher availability of striatal dopamine D2 receptors has been linked with decreased impulsivity and poor impulse control has, in turn, been suggested to make it difficult for one to enter and maintain a flow state.

In their recent study, de Manzano et al. (2012) measured how prone a group of 25 healthy volunteers were to flow experiences at work, household maintenance, and leisure time using the so-called Swedish Flow Proneness Questionnaire. In this questionnaire, there are several questions (for example “When you do something at work, how often does it happen that you feel completely concentrated?” that subjects are to score on a five-point Likert scale from “never” to “every day or almost every day”). One year prior to administration of this questionnaire, the same subjects had undergone positron emission tomography measurement of striatal dopamine D2 receptor binding potential with radioligand [11C]raclopride.

The authors observed a positive correlation between striatal D2 receptor binding potential and scores of the Flow Proneness Questionnaire. Further analyses focusing on subregions of the striatum showed that this correlation specifically involved dorsal striatum (i.e., caudate nucleus and putamen). These findings are highly interesting and provide the first demonstration that the degree a person is prone to experience flow states correlates with inter-individual differences in brain biochemistry. Based on these findings, the authors suggest that flow proneness might be related to higher impulse control due to higher dopamine D2 receptor binding potential making it easier to enter and maintain flow states. Overall, this study provides a highly interesting and important pioneering finding on the neural basis of flow states that clearly warrants further research.

Reference: de Manzano Ö, Cervenka S, Jucaite A, Hellenäs O, Farde L, Ullén F. Individual differences in the proneness to have flow experiences are linked to dopamine D2-receptor availability in the dorsal striatum. Neuroimage (2012) e-publication ahead of print. http://dx.doi.org/10.1016/j.neuroimage.2012.10.072