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Member-Initiated Symposia2012 Symposia Distinguishing perceptual shifts from response biases Human visual cortex: from receptive fields to maps to clusters to perception Neuromodulation of Visual Perception Part-whole relationships in visual cortex Pulvinar and Vision: New insights into circuitry and function What does fMRI tell us about brain homologies?
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Neuromodulation of Visual PerceptionFriday, May 11, 3:30 - 5:30 pm Organizers: Jutta Billino, Justus-Liebig-University Giessen and Ulrich Ettinger, Rheinische Friedrich-Wilhelms-Universität Bonn
Symposium DescriptionOver the last decades insights into the neurobiological mechanisms of
visual perception have accumulated an impressive knowledge base. However, only
recently research has started to uncover how different neurotransmitters affect
visual processing. Advances in this research area expand our understanding of
the complex regulation of sensory and sensorimotor processes. They moreover
shed light on the mechanisms underlying individual differences in visual
perception and oculomotor control that have been repeatedly observed, but are
still insufficiently understood. The symposium aims to bring together experts
in the field that complement each other with regard to different
neurotransmitter systems, methods, and implications of their findings. Thus,
the audience will be provided with an up-to-date overview of our knowledge on
neuromodulation of visual perception. The symposium will start with
presentations on physiological data showing the complexity of neuromodulation
in early visual cortex. Anita Disney (Salk Institute) has worked together with
Mike Hawken (New York University) on cholinergic mechanisms in macaque V1.
Their findings show that nicotinergic receptors for acetylcholine are involved
in gain modulation. The effects of nicotine application resemble those of
attention in the awake monkey. Thus, it has been suggested that attentional
effects in V1 activity might be partly mediated by acetylcholine. The
presentation by Alexander Thiele and colleagues (Newcastle University) will tie
in with the focus on attention. They have studied differential contributions of
acetylcholine and glutamate to attentional modulation in V1. They were able to
show that both neurotransmitters independently influence firing characteristics
of V1 neurons associated with enhanced attention. The work of Behrad Noudoost
and Tirin Moore (Stanford University) addresses prefrontal control of visual
cortical signals mediated by dopamine. Their findings reveal that dopaminergic
manipulation in the frontal eye fields does not only affect saccadic target
selection, but also modulates response characteristics of V4 neurons. In the
second part of the symposium presentations are supposed to bridge the gap
between insights from physiology and behavioral data in humans. Ariel Rokem
(Stanford University) and Michael Silver (UC Berkeley) pharmacologically
enhanced cholinergic transmission in healthy humans and studied perceptual
learning. Results support that acetylcholine increases the effects of
perceptual learning which points to its role in regulation of neural
plasticity. Ulrich Ettinger (Ludwig-Maximilians-University Munich) will
summarize his work on the modulation of oculomotor control by cholinergic and
dopaminergic challenges. He has studied effects of pharmacological manipulation
as well as of functional genetics on saccadic eye movements. His methods also
include imaging and clinical neuropsychology. The symposium will be completed
by a presentation of Patrick Bennett and Allison Sekuler (McMaster University)
on age-related changes in visual perception and how these can be modeled by
altered neurotransmitter activity. The symposium on neuromodulation of visual
perception will attract a broad audience because it offers a comprehensive and
interdisciplinary overview of recent advances in this innovative research area.
Presentations cover fundamental mechanisms of visual processing as well as
implications for perception and visuomotor control. Attendees with diverse
backgrounds will benefit and will be inspired to apply insights into
neuromodulation to their own research field. Presentations Modulating visual gain: cholinergic mechanisms in macaque V1
Anita A. Disney, Salk Institute
Michael J. Hawken, Center for Neural Science, New York University
Differential contribution of cholinergic and glutamatergic receptors to
attentional modulation in V1
Alexander Thiele, Institute of Neuroscience, Newcastle
University, Newcastle Upon Tyne, United Kingdom In V1, attentional modulation of firing rates is dependent on
cholinergic (muscarinic) mechanisms (Herrero et al., 2008). Modelling suggests
that appropriate ACh drive enables top-down feedback from higher cortical areas
to exert its influence (Deco & Thiele, 2011). The implementation of such
feedback at the transmitter/receptor level is poorly understood, but it is
generally assumed that feedback relies on ionotropic glutamatergic (iGluR)
mechanisms. We investigated this possibility by combining iontophoretic
pharmacological analysis with V1 cell recordings while macaques performed a
spatial attention task. Blockade or activation of iGluR did not alter
attention-induced increases in firing rate, when compared to attend away
conditions. However, attention reduced firing rate variance as previously
reported in V4 (Mitchell, Sundberg, Reynolds, 2007), and this reduction
depended on functioning iGluRs. Attention also reduced spike coherence between
simultaneously recorded neurons in V1 as previously demonstrated for V4 (Cohen
& Maunsell, 2009; Mitchell et al., 2007). Again, this reduction depended on
functional iGluR. Thus overall excitatory drive (probably aided by feedback),
increased the signal to noise ratio (reduced firing rate variance) and reduced
redundancy of information transmission (noise correlation) in V1. Conversely,
attention induced firing rate differences are enabled by the cholinergic
system. These studies identify independent contributions of different
neurotransmitter systems to attentional modulation in V1. Dopamine-mediated prefrontal control of visual cortical signals
Behrad Noudoost, Department of Neurobiology, Stanford
University School of Medicine Prefrontal cortex (PFC) is believed to play a crucial role in
executive control of cognitive functions. Part of this control is thought to be
achieved by control of sensory signals in posterior sensory cortices. Dopamine
is known to play a role in modulating the strength of signals within the PFC.
We tested whether this neurotransmitter is involved in PFC’s top-down control
of signals within posterior sensory areas. We recorded responses of neurons in
visual cortex (area V4) before and after infusion of the D1 receptor
(D1R)-antagonist SCH23390 into the frontal eye field (FEF) in monkeys
performing visual fixation and saccadic target selection tasks. Visual stimuli
were presented within the shared response fields of simultaneously studied V4
and FEF sites. We found that modulation of D1R-mediated activity within the FEF
enhances the strength of visual signals in V4 and increases the monkeys’
tendency to choose targets presented within the affected part of visual space.
Similar to the D1R manipulation, modulation of D2R-mediated activity within the
FEF also increased saccadic target selection. However, it failed to alter
visual responses within area V4. The observed effects of D1Rs in mediating the
control of visual cortical signals and the selection of visual targets, coupled
with its known role in working memory, suggest PFC dopamine as a key player in
the control of cognitive functions. Cholinergic enhancement of perceptual learning in the human visual system
Ariel Rokem, Department of Psychology, Stanford
University, Michael A. Silver, Helen Wills Neuroscience Institute and School of
Optometry, University of California, Berkeley Learning from experience underlies our ability to adapt to novel tasks
and unfamiliar environments. But how does the visual system know when to adapt
and change and when to remain stable? The neurotransmitter acetylcholine (ACh)
has been shown to play a critical role in cognitive processes such as attention
and learning. Previous research in animal models has shown that plasticity in
sensory systems often depends on the task relevance of the stimulus, but
experimentally increasing ACh in cortex can replace task relevance in inducing
experience-dependent plasticity. Perceptual learning (PL) is a specific and
persistent improvement in performance of a perceptual task with training. To
test the role of ACh in PL of visual discrimination, we pharmacologically
enhanced cholinergic transmission in the brains of healthy human participants
by administering the cholinesterase inhibitor donepezil (trade name: Aricept),
a commonly prescribed treatment for Alzheimer’s disease. To directly evaluate
the effect of cholinergic enhancement, we conducted a double-blind,
placebo-controlled cross-over study, in which each subject participated in a
course of training under placebo and a course of training under donepezil. We
found that, relative to placebo, donepezil increased the magnitude and
specificity of the improvement in perceptual performance following PL. These
results suggest that ACh plays a role in highlighting occasions in which
learning should occur. Specifically, ACh may regulate neural plasticity by
selectively increasing responses of neurons to behaviorally relevant stimuli. Pharmacological Influences on Oculomotor Control in Healthy Humans
Ulrich Ettinger, Rheinische Friedrich-Wilhelms-Universität Bonn Oculomotor control can be studied as an important model system for our
understanding of how the brain implements visually informed (reflexive and
voluntary) movements. A number of paradigms have been developed to investigate
specific aspects of the cognitive and sensorimotor processes underlying this
fascinating ability of the brain. For example, saccadic paradigms allow the
specific and experimentally controlled study of response inhibition as well as
temporo-spatial prediction. In this talk I will present recent data from
studies investigating pharmacological influences on saccadic control in healthy
humans. Findings from nicotine studies point to improvements of response
inhibition and volitional response generation through this cholinergic agonist.
Evidence from methylphenidate on the other hand suggests that oculomotor as
well as motor response inhibition is unaffected by this dopaminergic
manipulation, whereas the generation of saccades to temporally predictive
visual targets is improved. These findings will be integrated with our
published and ongoing work on the molecular genetic correlates of eye movements
as well as their underlying brain activity. I will conclude by (1) summarising
the pharmacological mechanisms underlying saccadic control and (2) emphasising
the role that such oculomotor tasks may play in the evaluation of potential
cognitive enhancing compounds, with implications for neuropsychiatric
conditions such as ADHD, schizophrenia and dementia. The effects of aging on GABAergic mechanisms and their influence on visual
perception
Patrick J. Bennett and Allison B. Sekuler, Department of
Psychology, Neuroscience & Behaviour McMaster University
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