SIR — We applaud your commitment, as
expressed in the Editorial “Peer review
and fraud” (Nature 444, 971–972; 2006),
to raising peer-reviewer awareness about
detecting fraud. For studies involving
humans, independent research ethics
committees (in the United States, institutional
review boards) provide
the first independent critical scrutiny of
research protocols. We recently examined
the instructions to authors of 103 medical
journals and found that none requires authors
to provide to readers (as online
supplementary information accompanying
the publication) the protocols approved by
As concern increases about the integrity of
published scientific research, we believe that
biomedical journals should establish a new
standard in human-research transparency.
They should require authors to state at
submission — and, where judged necessary,
in their published articles — that the research
has been approved by the relevant ethical
committees. All journals publishing
research on non-human animals (“Animal
experiments under fire for poor design”
Nature 444, 981; 2006) should do the same for
non-human animal protocols.
Journals should also require authors
to provide the full protocols approved by
these committees for the editors and peer
reviewers, and to allow the journal, if it
wishes, to publish these protocols as online
supplementary information accompanying
publication of the main paper.
Robert P. Dellavalle*†, Kristy Lundahl†,
Scott R. Freeman†, Lisa M. Schilling†
*Department of Veterans Affairs Medical Center,
1055 Clermont St, Denver, Colorado 80220, USA
†University of Colorado at Denver and Health
Sciences Center, Aurora, Colorado, USA
Tuesday, January 30, 2007
SIR — We applaud your commitment, as
Navindra Persaud, Peter McLeod & Alan Cowey
NATURE NEUROSCIENCE VOLUME 10, NUMBER 2, FEBRUARY 2007
The lack of an accepted measure of awareness has made
claims that accurate decisions can be made without awareness
controversial. Here we introduce a new objective measure of
awareness, post-decision wagering. We show that participants
fail to maximize cash earnings by wagering high following
correct decisions in blindsight, the Iowa gambling task and
an artificial grammar task. This demonstrates, without the
uncertainties associated with the conventional subjective
measures of awareness (verbal reports and confidence ratings),
that the participants were not aware that their decisions were
correct. Post-decision wagering may be used to study the
neural correlates of consciousness.
Also see the comment by Christof Koch: http://www.nature.com/neuro/journal/v10/n2/pdf/nn0207-140.pdf
Monday, January 29, 2007
Properties of shape tuning of macaque inferior temporal neurons examined using Rapid Serial Visual Presentation
De Baene W, Premereur E, Vogels R.
J Neurophysiol. 2007 Jan 24;
We used Rapid Serial Visual Presentation (RSVP) to examine the tuning of macaque inferior temporal cortical (IT) neurons to 5 sets of 25 shapes each that varied systematically along pre-defined shape dimensions. A comparison of the RSVP technique using 100 ms presentations with that using a longer duration showed that shape preference can be determined with RSVP. Using relatively complex shapes that vary along relatively simple shape dimensions, we found that the large majority of neurons preferred extremes of the shape configuration, extending the results of a previous study using simpler shapes and a standard testing paradigm (Kayaert et al. 2005). A population analysis of the neuronal responses demonstrated that, in general, IT neurons can represent the similarities among the shapes at an ordinal level, extending a previous study that used a smaller number of shapes and a categorization task (Op de Beeck et al. 2001). However, the same analysis showed that IT neurons do not faithfully represent the physical similarities among the shapes. The responses to the two-part shapes could be predicted, virtually perfectly, from the average of the responses to the respective two parts presented in isolation. We also showed that IT neurons adapt to the stimulus distribution statistics. The neural shape discrimination improved when a shape set with a narrower stimulus range was presented, suggesting that the tuning of IT neurons is not static but adapts to the stimulus distribution statistics, at least when stimulated at a high rate with a restricted set of stimuli.
Jennifer Singh, Joachim Hallmayer, Judy Illes
Nature Reviews Neuroscience 8, 153-160 (February 2007) | doi:10.1038/nrn2073
Discoveries in the field of neuroscience are a natural source of discourse among scientists and have long been disseminated to the public. Historically, as news of findings has travelled between communities, it has elicited both expected and unusual reactions. What scientific landmarks promote discourse within the professional community? Do the same findings achieve a place in the public eye? How does the media choose what is newsworthy, and why does the public react the way it does? Drawing on examples of past challenges at the crossroads of neuroscience and society and on a case study of trends in one neurogenetic disease, autism, we explore the dialectical forces interacting in scientific and public discourse.
Peter Redgrave,Kevin Gurney
Nature Reviews Neuroscience 7, 967-975 (December 2006) | doi:10.1038/nrn2022
An influential concept in contemporary computational neuroscience is the reward prediction error hypothesis of phasic dopaminergic function. It maintains that midbrain dopaminergic neurons signal the occurrence of unpredicted reward, which is used in appetitive learning to reinforce existing actions that most often lead to reward. However, the availability of limited afferent sensory processing and the precise timing of dopaminergic signals suggest that they might instead have a central role in identifying which aspects of context and behavioural output are crucial in causing unpredicted events.
Mechler F, Ohiorhenuan IE, Victor JD.
J Neurophysiol. 2007 Jan 24;
Using drifting compound grating stimuli matched in energy and frequency spectrum, we previously showed (Mechler et al. 2002) that neurons in the primary visual cortex (V1) were tuned to line-like, edge-like, and intermediate one-dimensional features. Because these compound grating stimuli were drifting, allowing for potential interaction between shape and motion, we examine here the dependence of V1 feature tuning on drift speed. We find that the feature selectivity and specificity of individual V1 neurons strongly depend on speed. A simple model explains these observations in terms of an interaction between linear filtering by the receptive field and the static nonlinearity of spike threshold, embedded in a recurrent network. While the speed-dependent behaviors in single V1 neurons preclude their acting as extractors of one-dimensional features, the population as a whole retains a representation of a full suite of features.
Sunday, January 28, 2007
Shifts in Coding Properties and Maintenance of Information Transmission during Adaptation in Barrel Cortex
Maravall M, Petersen RS, Fairhall AL, Arabzadeh E, Diamond ME
Neuronal responses to ongoing stimulation in many systems change over time, or "adapt." Despite the ubiquity of adaptation, its effects on the stimulus information carried by neurons are often unknown. Here we examine how adaptation affects sensory coding in barrel cortex. We used spike-triggered covariance analysis of single-neuron responses to continuous, rapidly varying vibrissa motion stimuli, recorded in anesthetized rats. Changes in stimulus statistics induced spike rate adaptation over hundreds of milliseconds. Vibrissa motion encoding changed with adaptation as follows. In every neuron that showed rate adaptation, the input-output tuning function scaled with the changes in stimulus distribution, allowing the neurons to maintain the quantity of information conveyed about stimulus features. A single neuron that did not show rate adaptation also lacked input-output rescaling and did not maintain information across changes in stimulus statistics. Therefore, in barrel cortex, rate adaptation occurs on a slow timescale relative to the features driving spikes and is associated with gain rescaling matched to the stimulus distribution. Our results suggest that adaptation enhances tactile representations in primary somatosensory cortex, where they could directly influence perceptual decisions.
FREE Fulltext: http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1779810&blobtype=pdf
Posted by Ali at 8:38 AM
J. Patrick Mayo
Every minute, we sweep our eyes over
multiple objects. We look at one object
and then another, shifting our gaze across
cluttered scenes when, for example,
searching a desktop for car keys. Such real
world complexities are difficult to model
in the laboratory. Instead, a single stimulus
is often used to characterize visual responses
of neurons, be it a small bar in
primary visual cortex (V1) or a threedimensional
object in “higher” cortical
areas in the inferotemporal (IT) and frontal
lobes. Forays into more complex tasks
using multiple stimuli have mainly been
limited to simultaneously presented stimuli
in search and visual clutter tasks. Remarkably
few studies have investigated
how visual cortices respond to sequential
stimulus presentations. This paucity of research
is surprising given the wealth of
data collected in the psychophysical literature
regarding the temporal phenomena
of visual masking and inhibition of return.
A recent paper in the Journal of Neuroscience
(Motter, 2006) begins to fill this
conceptual void. The author recorded
from visual area V4 in awake behaving
monkeys while long sequences of stimuli
Wednesday, January 17, 2007
Structural Imaging Reveals Anatomical Alterations in Inferotemporal Cortex in Congenital Prosopagnosia
Behrmann, Avidan, Gao, Black.
Cereb Cortex. 2007 Jan 11;
Department of Psychology, Carnegie Mellon University, Pittsburgh, PA 15213-3890, USA.
Congenital prosopagnosia (CP) refers to the lifelong impairment in face recognition in individuals who have intact low-level visual processing, normal cognitive abilities, and no known neurological disorder. Although the face recognition impairment is profound and debilitating, its neural basis remains elusive. To investigate this, we conducted detailed morphometric and volumetric analyses of the occipitotemporal (OT) cortex in a group of CP individuals and matched control subjects using high-spatial resolution magnetic resonance imaging. Although there were no significant group differences in the depth or deviation from the midline of the OT or collateral sulci, the CP individuals evince a larger anterior and posterior middle temporal gyrus and a significantly smaller anterior fusiform (aF) gyrus. Interestingly, this volumetric reduction in the aF gyrus is correlated with the behavioral decrement in face recognition. These findings implicate a specific cortical structure as the neural basis of CP and, in light of the familial history of CP, target the aF gyrus as a potential site for further, focused genetic investigation.
Posted by Ali at 10:12 PM
Top 100 papers in Vision Science
Posted by Ali at 9:39 PM
Tuesday, January 16, 2007
Thanks for inviting me in your weblog, specially my dear Ali ... And I'm sorry for the the terrible mess I'm going to make of your weblog in advance. My condolences!
OK, I don't know what can be said and what not in this weblog, so I save my jokes and introduce you scientific craps:
Recently, say January 2007, an almost decent, very-well-IF-scored journal called "Neuropsychologia" published a special issue on face perception. You can find some famous names like James Haxby, Edmund T. Rolls among editors and authors.
Ed Rolls has a review article in this issue which is from cover to cover about his works and papers as you may guess. But it is a Pretty good one:
Edmund T. Rolls
The representation of information about faces in the temporal and frontal lobes.
Neuropsychologia Volume 45, Issue 1 , 2007, Pages 124-143 The Perception of Emotion and Social Cues in Faces
You may find another interesting paper as fun stuff in this issue by David I. Perrett. At least you can evaluate you GF with it if know enough about advance math the paper used.
Brain systems for assessing facial attractiveness.
Neuropsychologia Volume 45, Issue 1 , 2007, Pages 195-206
OK, That's all.
Retrograde neuronal tracing with a deletion-mutant rabies virus
Ian R Wickersham, Stefan Finke, Karl-Klaus Conzelmann & Edward M Callaway
Posted by Mehdi at 12:30 PM
Saturday, January 13, 2007
Robbe, Montgomery, Thome, Rueda-Orozco1, McNaughton, Buzsaki
Nature Neuroscience, V9 N12, Dec 2006
Cannabinoids impair hippocampus-dependent memory in both humans and animals, but the network mechanisms responsible for this effect are unknown. Here we show that the cannabinoids D9-tetrahydrocannabinol and CP55940 decreased the power of theta, gamma and ripple oscillations in the hippocampus of head-restrained and freely moving rats. These effects were blocked by a CB1 antagonist. The decrease in theta power correlated with memory impairment in a hippocampus-dependent task. By simultaneously recording from large populations of single units, we found that CP55940 severely disrupted the temporal coordination of cell assemblies in short time windows ( < 100 ms) yet only marginally affected population firing rates of pyramidal cells and interneurons. The decreased power of local field potential oscillations correlated with reduced temporal synchrony but not with firing rate changes. We hypothesize that reduced spike timing coordination and the associated impairment of physiological oscillations are responsible for cannabinoid-induced memory deficits.
Posted by Ali at 1:33 PM
Monday, January 8, 2007
Separate Coding of Different Gaze Directions in the Superior Temporal Sulcus and Inferior Parietal Lobule
Calder, Beaver, Winston, Dolan, Jenkins, Eger, Henson
Current Biology, Vol 17, 20-25, 09 January 2007
Electrophysiological recording in the anterior superior temporal sulcus (STS) of monkeys has demonstrated separate cell populations responsive to direct and averted gaze [1, 2]. Human functional imaging has demonstrated posterior STS activation in gaze processing, particularly in coding the intentions conveyed by gaze [3, 4, 5, 6], but to date has provided no evidence of dissociable coding of different gaze directions. Because the spatial resolution typical of group-based fMRI studies (∼6–10 mm) exceeds the size of cellular patches sensitive to different facial characteristics (1–4 mm in monkeys), a more sensitive technique may be required. We therefore used fMRI adaptation, which is considered to offer superior resolution , to investigate whether the human anterior STS contains representations of different gaze directions, as suggested by non-human primate research. Subjects viewed probe faces gazing left, directly ahead, or right. Adapting to leftward gaze produced a reduction in BOLD response to left relative to right (and direct) gaze probes in the anterior STS and inferior parietal cortex; rightward gaze adaptation produced a corresponding reduction to right gaze probes. Consistent with these findings, averted gaze in the adapted direction was misidentified as direct. Our study provides the first human evidence of dissociable neural systems for left and right gaze.
Full text: http://www.current-biology.com/content/article/abstract?uid=PIIS0960982206024274
Posted by Ali at 11:55 PM
Sunday, January 7, 2007
Impact of Experience on the Representation of Object-Centered Space in the Macaque Supplementary Eye Field.
Many neurons in the macaque supplementary eye field (SEF) exhibit object-centered spatial selectivity, firing at different rates when the monkey plans a saccade to the left or right end of a horizontal bar. Is this property natural to the supplementary eye field or is it a product of specialized training in the laboratory? To answer this question, we monitored the activity of single SEF neurons in two monkeys before and after training to select eye-movement targets by an object-centered rule. During stage 1, the monkeys performed a color delayed-match-to-sample (DMS) task in which a red or green central cue dictated an eye movement to the matching end of a horizontal bar. Many neurons at this stage exhibited object-centered spatial selectivity. During stage 2, the monkeys performed a color-conditional object-centered task in which a green or red central cue instructed an eye movement to the left or right end of a gray bar. More neurons exhibited object-centered spatial selectivity during this stage than during stage 1. During stage 3, the monkeys again performed the color DMS task. The fraction of neurons exhibiting object-centered spatial selectivity remained at a level comparable to that observed during stage 2 and above that observed during stage 1. Thus object-centered spatial selectivity was present before training on an object-centered rule, was enhanced as a product of object-centered training, and outlasted active use of an object-centered rule. We conclude that neural representations of object-centered space, naturally present in the primate brain, can be sharpened by training.
Posted by Ali at 9:13 AM
این هم یک review برای دوست داران LIP .
فارسی و انگلیسی مخلوط هم بعضی وقتها ظاهر نامناسبی پیدا می کنه!
Neuron. 2007 Jan
The lateral intraparietal area (LIP) is a subdivision of the inferior parietal lobe that has been implicated in the guidance of spatial attention. In a variety of tasks, LIP provides a "salience representation" of the external world-a topographic visual representation that encodes the locations of salient or behaviorally relevant objects. Recent neurophysiological experiments show that this salience representation incorporates information about multiple behavioral variables-such as a specific motor response, reward, or category membership-associated with the task-relevant object. This integration occurs in a wide variety of tasks, including those requiring eye or limb movements or goal-directed or nontargeting operant responses. Thus, LIP acts as a multifaceted behavioral integrator that binds visuospatial, motor, and cognitive information into a topographically organized signal of behavioral salience. By specifying attentional priority as a synthesis of multiple task demands, LIP operates at the interface of perception, action, and cognition.
Posted by Ali at 8:49 AM
Wilke M, Logothetis NK, Leopold DA.
PNAS November 14 2006
Neurophysiological and functional imaging experiments remain in apparent disagreement on the role played by the earliest stages of the visual cortex in supporting a visual percept. Here, we report electrophysiological findings that shed light on this issue. We monitored neural activity in the visual cortex of monkeys as they reported their perception of a high-contrast visual stimulus that was induced to vanish completely from perception on a subset of trials. We found that the spiking of neurons in cortical areas V1 and V2 was uncorrelated with the perceptual visibility of the target, whereas that in area V4 showed significant perception-related changes. In contrast, power changes in the lower frequency bands (particularly 9-30 Hz) of the local field potential (LFP), collected on the same trials, showed consistent and sustained perceptual modulation in all three areas. In addition, for the gamma frequency range (30-50 Hz), the responses during perceptual suppression of the target were correlated significantly with the responses to its physical removal in all areas, although the modulation magnitude was considerably higher in area V4 than in V1 and V2. These results, taken together, suggest that low-frequency LFP power in early cortical processing is more closely related to the representation of stimulus visibility than is spiking or higher frequency LFP activity.
Full text: http://www.pnas.org/cgi/reprint/103/46/17507
Posted by Ali at 1:32 AM
Plos Biology - November 2006
The sensory-triggered activity of a neuron is typically characterized in terms of a tuning curve, which describes the neuron's average response as a function of a parameter that characterizes a physical stimulus. What determines the shapes of tuning curves in a neuronal population? Previous theoretical studies and related experiments suggest that many response characteristics of sensory neurons are optimal for encoding stimulus-related information. This notion, however, does not explain the two general types of tuning profiles that are commonly observed: unimodal and monotonic. Here I quantify the efficacy of a set of tuning curves according to the possible downstream motor responses that can be constructed from them. Curves that are optimal in this sense may have monotonic or nonmonotonic profiles, where the proportion of monotonic curves and the optimal tuning-curve width depend on the general properties of the target downstream functions. This dependence explains intriguing features of visual cells that are sensitive to binocular disparity and of neurons tuned to echo delay in bats. The numerical results suggest that optimal sensory tuning curves are shaped not only by stimulus statistics and signal-to-noise properties but also according to their impact on downstream neural circuits and, ultimately, on behavior.
Full text: http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0040387
Posted by Ali at 1:27 AM
چه می کنه این تکنیک های ملکولار بیولوژی وقتی دست الکترفیزیولوژیستها می افته!
Laplagne, Espo´ sito, Piatti, Morgenstern, Zhao, Praag, Gage, Schinder
Plos Biology - December 2006
The dentate gyrus of the hippocampus contains neural progenitor cells (NPCs) that generate neurons throughout life. Developing neurons of the adult hippocampus have been described in depth. However, little is known about their functional properties as they become fully mature dentate granule cells (DGCs). To compare mature DGCs generated during development and adulthood, NPCs were labeled at both time points using retroviruses expressing different
fluorescent proteins. Sequential electrophysiological recordings from neighboring neurons of different ages were carried out to quantitatively study their major synaptic inputs: excitatory projections from the entorhinal cortex and inhibitory afferents from local interneurons. Our results show that DGCs generated in the developing and adult hippocampus display a remarkably similar afferent connectivity with regard to both glutamate and GABA, the major neurotransmitters. We also demonstrate that adult-born neurons can fire action potentials in response to an excitatory drive, exhibiting a firing behavior comparable to that of neurons generated during development. We propose that neurons born in the developing and adult hippocampus constitute a functionally homogeneous neuronal population.
These observations are critical to understanding the role of adult neurogenesis in hippocampal function.
Free Fulltext: http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0040409
Posted by Ali at 12:31 AM
Have a look at the http://biology.plosjournals.org/ the Plos Biology home page. Specifically note the open access section.
Here people can publish with minimal per publishing peer review. After online publication of the paper, the scientific community would comment on it, it is an open access peer review system which allows everyone to read and comment on the others papers. After a year or more "ُسیه روی شود هر که در او غش باشد"
Posted by Ali at 12:21 AM
Saturday, January 6, 2007
This is a modification of a figure form a paper by Saleem, Suzuki, Tanaka, Hashikawa titled "Connections between Anterior Inferotemporal Cortex and Superior Temporal Sulcus Regions in the Macaque Monkey" published in J Neuroscie 2000.
In fact it is superimposed on a negative version of a photo-microscopic image of a cortical region (Courtesy of Kathlin Rockland)
Posted by Ali at 11:34 PM
Exploring the neural basis of cognition: multi-modal links between human fMRI and macaque neurophysiology
Nakahara K, Adachi Y, Osada T, Miyashita Y.
Trends Cogn Sci. 2006 Dec 22
Although functional magnetic resonance imaging (fMRI) with sophisticated behavioral paradigms has enabled the investigation of increasingly higher-level cognitive functions in humans, these studies seem to lose touch with neurophysiological studies in macaque monkeys. The application of fMRI and other MRI-based techniques to macaque brains allows studies in the two species to be linked. fMRI in human and macaque subjects using equivalent cognitive tasks enables direct comparisons of the functional brain architecture, even for high-level cognitive functions. Combinations of functional or structural MRI and microelectrode techniques provide ways to explore functional brain networks at multiple spatiotemporal scales. These approaches would illuminate the neurophysiological underpinnings of human cognitive functions by integrating human functional neuroimaging with macaque single-unit recordings.
Posted by Ali at 1:37 AM
Szpunar KK, Watson JM, McDermott KB.
Proc Natl Acad Sci U S A. 2007 Jan 3
The ability to envision specific future episodes is a ubiquitous mental phenomenon that has seldom been discussed in the neuroscience literature. In this study, subjects underwent functional MRI while using event cues (e.g., Birthday) as a guide to vividly envision a personal future event, remember a personal memory, or imagine an event involving a familiar individual. Two basic patterns of data emerged. One set of regions (e.g., within left lateral premotor cortex; left precuneus; right posterior cerebellum) was more active while envisioning the future than while recollecting the past (and more active in both of these conditions than in the task involving imagining another person). These regions appear similar to those emerging from the literature on imagined (simulated) bodily movements. A second set of regions (e.g., bilateral posterior cingulate; bilateral parahippocampal gyrus; left occipital cortex) demonstrated indistinguishable activity during the future and past tasks (but greater activity in both tasks than the imagery control task); similar regions have been shown to be important for remembering previously encountered visual-spatial contexts. Hence, differences between the future and past tasks are attributed to differences in the demands placed on regions that underlie motor imagery of bodily movements, and similarities in activity for these two tasks are attributed to the reactivation of previously experienced visual-spatial contexts. That is, subjects appear to place their future scenarios in well known visual-spatial contexts. Our results offer insight into the fundamental and little-studied capacity of vivid mental projection of oneself in the future
Free Fulltext: http://www.pnas.org/cgi/reprint/0610082104v1
Oscillatory Activity in Human Parietal and Occipital Cortex Shows Hemispheric Lateralization and Memory Effects in a Delayed Double-Step Saccade Task
Medendorp WP, Kramer GF, Jensen O, Oostenveld R, Schoffelen JM, Fries P.
Cereb Cortex. 2006 Dec 26
We applied magnetoencephalography (MEG) to record oscillatory brain activity from human subjects engaged in planning a double-step saccade. In the experiments, subjects (n = 8) remembered the locations of 2 sequentially flashed targets (each followed by a 2-s delay), presented in either the left or right visual hemifield, and then made saccades to the 2 locations in sequence. We examined changes in spectral power in relation to target location (left or right) and memory load (one or two targets), excluding error trials based on concurrent eye tracking. During the delay period following the first target, power in the alpha (8-12 Hz) and beta (13-25 Hz) bands was significantly suppressed in the hemisphere contralateral to the target. When the second target was presented, there was a further suppression in the alpha- and beta-band power over both hemispheres. In this period, the same sensors also showed contralateral power enhancements in the gamma band (60-90 Hz), most significantly prior to the initiation of the saccades. Adaptive spatial filtering techniques localized the neural sources of the directionally selective power changes in parieto-occipital areas. These results provide further support for a topographic organization for delayed saccades in human parietal and occipital cortex.
Free Fulltext: http://cercor.oxfordjournals.org/cgi/reprint/bhl145v1
Friday, January 5, 2007
Nancy Kanwisher1, Galit Yovel
A comprehensive review of face recognition literature, with focus on human data.
Phil. Trans. R. Soc. B (2006) 361, 2109–2128
Thursday, January 4, 2007
Giedrius T. Buracas and Geoffrey M. Boynton
Previous electrophysiology data suggests that the modulation of neuronal firing by spatial attention depends on stimulus contrast, which
has been described using either a multiplicative gain or a contrast-gain model. Herewemeasured the effect of spatial attention on contrast
responses in humans using functional MRI. To our surprise, we found that the modulation of blood oxygenation level-dependent (BOLD)
responses by spatial attention does not greatly depend on stimulus contrast in visual cortical areas tested [V1, V2, V3, andMT(middle
temporal area)]. An additive model, rather than a multiplicative or contrast-gain model best describes the attentional modulations in V1.
This inconsistency with previous single-unit electrophysiological data has implications for the population-based neuronal source of the