Generative models, brain function and neuroimaging

The representational capacity and inherent function of any neuron, neuronal population or cortical area in the brain is dynamic and context-sensitive. Functional integration, or interactions among brain systems, that employ driving (bottom up) and backward (top-down) connections, mediate this adaptive and contextual specialisation. A critical consequence is that neuronal responses, in any given cortical area, can represent different things at different times. This can have fundamental implications for the design of brain imaging experiments and the interpretation of their results. Our arguments are developed under generative models of brain function, where higher-level systems provide a prediction of the inputs to lower-level regions. Conflict between the two is resolved by changes in the higher-level representations, which are driven by the ensuing error in lower regions, until the mismatch is "cancelled". From this perspective the specialisation of any region is determined both by bottom-up driving inputs and by top-down predictions. Specialisation is therefore not an intrinsic property of any region but depends on both forward and backward connections with other areas. Because the latter have access to the context in which the inputs are generated they are in a position to modulate the selectivity or specialisation of lower areas. The implications for classical models (e.g., classical receptive fields in electrophysiology, classical specialisation in neuroimaging and connectionism in cognitive models) are severe and suggest these models may provide incomplete accounts of real brain architectures. Here we focus on the implications for cognitive neuroscience in the context of neuroimaging.     

Gaze direction and maternal pitch in surprise-eliciting situations

The purpose of this study was to test the hypothesis that not only do babies use emotional signals from adults in order to relate emotions to specific situations (e.g., Campos & Stenberg, 1981) but also that mothers seek out emotional information from their infants ( Emde, 1992). Three groups of mothers and their infants, 3, 5 and 9 months old were video- and audio-taped, while playing in their homes with a soft toy and a remote-control Jack-in-the-box. During surprise-eliciting play with the Jack-in-the-box, maternal and infant gaze direction and their emotional expressions of surprise, pleasure, fear and neutral expressions were coded in three regions of the face. In addition, the mean fundamental frequency of maternal surprise-vocalisations was analysed. Maternal exclamations of surprise were compared with similar utterances of these mothers while playing with a soft toy as a baseline. During the surprise event, maternal and infant gaze directions as well as infant age were analysed in relation to maternal pitch. Results are discussed in terms of maternal use of the pitch of her voice to mark surprising situations, depending on the gaze-direction of the infant.     

Gaze discrimination learning in olive baboons (Papio anubis)

The ability to discriminate between pairs of photographs according to the portrayed model's visual attention status was examined in four olive baboons. Two baboons successfully managed to solve the problem, even when attention was demonstrated by eye direction alone. A third showed an ability to discriminate head direction but not eye direction. In order to investigate further their ability to discriminate attention, the two successful baboons and two na?ve baboons were presented with a simple object-choice task accompanied by experimenter-given cues. There was no evidence of transfer from the photographic stimuli to a real model; only one baboon showed signs of using the experimenter's attention to chose between two objects, and only after over 300 trials. These results could suggest that the baboons used simple physical cues rather than a concept of attention to solve the picture discrimination but alternative explanations are also discussed. Accepted after revision: 5 February 2001 Electronic Publication     

Functional integration and the mind

Different cognitive functions recruit a number of different, often overlapping, areas of the brain. Theories in cognitive and computational neuroscience are beginning to take this kind of functional integration into account. The contributions to this special issue consider what functional integration tells us about various aspects of the mind such as perception, language, volition, agency, and reward. Here, I consider how and why functional integration may matter for the mind; I discuss a general theoretical framework, based on generative models, that may unify many of the debates surrounding functional integration and the mind; and I briefly introduce each of the contributions.     

Contextual learning induces an increase in the number of hippocampal CA1 neurons expressing high levels of BDNF

We examined behaviorally induced expression of brain-derived neurotrophic factor (BDNF) in area CA1 of the hippocampus. Sprague-Dawley rats were trained in a contextual fear conditioning (CFC) task, sacrificed 4h later, and their brains were processed for immunohistochemistry. We found distinctively high levels of BDNF immunoreactivity in a small number ( approximately 1%) of CA1 neurons in untrained animals. The number of these exceptional neurons, which are identified as BDNF(++) in this study, was increased by up to approximately 3% after CFC. This increase was blocked in the presence of a memory-impairing dose of a NMDA receptor antagonist (MK801 0.3 mg/kg, i.p.) given 30 min prior to training. The BDNF signal intensity in BDNF(++) neurons correlated with that of surrounding glutamic acid decarboxylase (GAD) 65. This correlation between GAD65 and BDNF signal intensities suggests that BDNF upregulation was associated with increased signaling via inhibitory GABAergic synapses that would lessen further intervening neuronal activity. Our observation that neurons which upregulate BDNF expression following a learning experience are rich in GAD65-enriched afferent synapses suggests that these neurons may have distinct roles in memory consolidation.     

I know you are not looking at me: capuchin monkeys’ (<Emphasis Type="Italic">Cebus apella</Emphasis>) sensitivity to human attentional states

The present study asked whether capuchin monkeys recognize human attentional states. The monkeys requested food from the experimenter by extending an arm (pointing) toward the baited one of two transparent cups. On regular trials the experimenter gave the food immediately to the monkeys upon pointing but on randomly inserted test trials she ignored the pointing for 5 s during which she displayed different attentional states. The monkeys looked at the experimenter's face longer when she looked at the monkeys than when she looked at the ceiling in Experiment 1, and longer when she oriented her head midway between the two cups with eyes open than when she did so with eyes closed in Experiment 2. However, the monkeys showed no differential pointing in these conditions. These results suggest that capuchins are sensitive to eye direction but this sensitivity does not lead to differential pointing trained in laboratory experiments. Furthermore, to our knowledge, this is the first firm behavioral evidence that non-human primates attend to the subtle states of eyes in a food requesting task.     

PyHab: Open-source real time infant gaze coding and stimulus presentation software

Infant looking-time paradigms often use specialized software for real time manual coding of infant gaze. Here, I introduce PyHab, the first open-source looking-time coding and stimulus presentation solution designed specifically with open science in mind. PyHab is built on the libraries of PsychoPy (Peirce, 2007). PyHab has its own graphical interface for building studies and requires no programming experience to use. When creating a study, PyHab saves a folder that contains all of the code required to run the study and all of the stimuli, making each experiment a self-contained, easily shared package. This feature guarantees the ability to replicate a PyHab experiment exactly as it was run. PyHab also has several features designed to support rigorous methodology, such as experimenter blinding and automatic stimulus control. In addition, because it is open-source, PyHab can be modified and improved not only by its developer but by anyone who knows Python.     

Response-repetition effects depend on motor set: Evidence for anatomical coding in response selection

Successful motor performance requires a process of response selection that chooses the correct response out of a set of possible ones. Most theories of response selection assume that this selection process operates on spatial codes, which define the location of stimuli and responses in environmental coordinates, with little or no role for the anatomical codes of the effectors involved. In this study, we tested this assumption by investigating response-repetition effects in a response-cuing paradigm using two motor sets (fingers on one hand vs. fingers on two hands). Reaction time results demonstrated a robust response-repetition benefit that was greater for the one-hand set than for the two-hands set. Furthermore, with the one-hand set the repetition benefit was independent of cue type and cue-stimulus interval on the previous trial, whereas with the two-hands set it was strongly modulated by these two factors. These differential response-repetition effects for one- and two-hands motor sets demonstrate the important role of the neuro-anatomical hand distinction in response selection, thereby supporting multiple coding notions.     

Gaze direction affects visuo-spatial short-term memory

Hemispheric asymmetries were investigated by changing the horizontal position of stimuli that had to be remembered in a visuo-spatial short-term memory task. Observers looked at matrices containing a variable number of filled squares on the left or right side of the screen center. At stimulus offset, participants reproduced the positions of the filled squares in an empty response matrix. Stimulus and response matrices were presented in the same quadrant. We observed that memory performance was better when the matrices were shown on the left side of the screen. We distinguished between recall strategies that relied on visual or non-visual (verbal) cues and found that the effect of gaze position occurred more reliably in participants using visual recall strategies. Overall, the results show that there is a solid enhancement of visuo-spatial short-term memory when observers look to the left. In contrast, vertical position had no influence on performance. We suggest that unilateral gaze to the left activates centers in the right hemisphere contributing to visuo-spatial memory.     

Implicit need for achievement predicts attenuated cortisol responses to difficult tasks

The present research tested the hypothesis that the implicit need for achievement (n Achievement) predicts attenuated cortisol (C) responses to difficult tasks, because it represents a propensity to view difficulty as a cue to mastery reward. In two studies, n Achievement was assessed through content-coding of imaginative stories and salivary C was assessed both at baseline and post-task. In Study 1 (N = 108 US students), n Achievement predicted an attenuated C response to a one-on-one competition in the laboratory, regardless of whether participants won or lost. In Study 2 (N = 62 German students), n Achievement predicted an attenuated C response to the Trier Social Stress Test (Kirschbaum, Pirke, & Hellhammer, 1993), but not to a non-stressful control task. In Study 2 only, the attenuating effect of n Achievement was moderated by gender, with only men showing the effect. Across both studies, the average effect size of the association between n Achievement and C responses to difficult tasks was r = −.28. These findings point to a role of n Achievement in emotion regulation.