Central olfactory connections in the macaque monkey

The connections between the olfactory bulb, primary olfactory cortex, and olfactory related areas of the orbital cortex were defined in macaque monkeys with a combination of anterograde and retrograde axonal tracers and electrophysiological recording. Anterograde tracers placed into the olfactory bulb labeled axons in eight primary olfactory cortical areas: the anterior olfactory nucleus, piriform cortex, ventral tenia tecta, olfactory tubercle, anterior cortical nucleus of the amygdala, periamygdaloid cortex, and olfactory division of the entorhinal cortex. The bulbar axons terminate in the outer part of layer I throughout these areas and are most dense in areas that are close to the lateral olfactory tract. Labeled axons also were found in the superficial part of nucleus of the horizontal diagonal band. Retrograde tracers injected into the olfactory bulb labeled cells in the nucleus of the diagonal band and in all of the primary olfactory cortical areas except the olfactory tubercle. Electrical stimulation of the olfactory bulb evoked short-latency unit responses and a characteristic field wave in the primary olfactory cortex. Multiunit activity in layer II tended to be of shorter latency than that in layer III and the endopiriform nucleus. Associational connections within the primary olfactory cortex were demonstrated with anterograde tracer injections into the piriform cortex and the entorhinal cortex. Injections into the piriform cortex near the lateral olfactory tract labeled axons in the deep part of layer I of many primary olfactory areas, but especially in areas near the tract. An injection into the rostral entorhinal cortex, distant to the lateral olfactory tract, labeled a complementary distribution of axons in deep layer I of olfactory areas medial and caudoventral to the tract. This organization resembles that reported in the primary olfactory cortex of the rat [Luskin and Price (1983) J. Comp. Neurol. 216:264-291]. The anterograde tracer injections into the piriform cortex and retrograde tracer injections into the orbital and medial prefrontal cortex and rostral insula label connections from the primary olfactory cortex to nine areas in the caudal orbital cortex, including the agranular insula areas Iam, Iai, Ial, Iapm, and Iapl and areas 14c, 25, 13a, and 13m. The piriform cortex projects most heavily to layer I of these areas. Only Iam, Iapm, and 13a receive a substantial projection to the deeper layers. Areas Iam, Iapm, and 13a were also the only areas that responded with multiunit action potentials to olfactory bulb stimulation in anesthetized animals.

Central olfactory connections in the macaque monkey
Carmichael ST, Clugnet MC, Price JL.
J Comp Neurol 1994 Aug 15;346(3):403-34

http://brainmeta.com/neuroanat/a16.html

Parallel-distributed Processing in Olfactory Cortex: New Insights from Morphological and Physiological Analysis of Neuronal Circuitry

A working hypothesis is proposed for piriform cortex (PC) and other olfactory cortical areas that redefines the traditional functional roles as follows: the olfactory bulb serves as the primary olfactory cortex by virtue of encoding ‘molecular features’ (structural components common to many odorant molecules) as a patchy mosaic reminiscent of the representation of simple features in primary visual cortex. The anterior olfactory cortex (that has been inappropriately termed the anterior olfactory nucleus) detects and stores correlations between olfactory features, creating representations (gestalts) for particular odorants and odorant mixtures. This function places anterior olfactory cortex at the level of secondary visual cortex. PC carries out functions that have traditionally defined association cortex—it detects and learns correlations between olfactory gestalts formed in anterior olfactory cortex and a large repertoire of behavioral, cognitive and contextual information to which it has access through reciprocal connections with prefrontal, entorhinal, perirhinal and amygdaloid areas. Using principles derived from artificial networks with biologically plausible parallel-distributed architectures and Hebbian synaptic plasticity (i.e. adjustments in synaptic strength based on locally convergent activity), functional proposals are made for PC and related cortical areas. Architectural features incorporated include extensive recurrent connectivity in anterior PC, predominantly feedforward connectivity in posterior PC and backprojections that connect distal to proximal structures in the cascade of olfactory cortical areas. Capabilities of the ‘reciprocal feedforward correlation’ architecture that characterizes PC and adjoining higher-order areas are discussed in some detail. The working hypothesis is preceded by a review of relevant anatomy and physiology, and a non-quantitative account of parallel-distributed principles. To increase the accessibility of findings for PC and to advertise its substantial potential as a model for experimental and modeling analysis of associative processes, parallels are described between PC and the hippocampal formation, inferotemporal visual cortex and prefrontal cortex.

Lewis B. Haberly
Parallel-distributed Processing in Olfactory Cortex: New Insights from Morphological and Physiological Analysis of Neuronal Circuitry
Chem. Senses 26: 551-576.

http://chemse.oxfordjournals.org/cgi/content/full/26/5/551

Multisensory and Secondary Somatosensory Cortex in the Rat

The function of secondary somatosensory (SII) cortex is poorly understood, but there is evidence to suggest that one of its roles may be in multisensory integration. This study used high-resolution field potential mapping coupled with laminar field potential and multiunit recording to examine the association between SII and multisensory (auditory–somatosensory) cortex in the rat. We demonstrate that while there is spatial overlap between unisensory areas of SII and multisensory regions, particularly for representations of the trunk and hind limbs, they form distinct somatotopic maps. We propose that multisensory cortex be considered functionally distinct from SII, and that SII may be more concerned with unisensory processing tasks.

Richard R. Menzel , and Daniel S. Barth
Multisensory and Secondary Somatosensory Cortex in the Rat
Cerebral Cortex Advance Access published on November 1, 2005, DOI 10.1093/cercor/bhi045.
Cereb. Cortex 15: 1690-1696.

http://cercor.oxfordjournals.org/cgi/content/full/15/11/1690

Insular Cortical Projections to Functional Regions of the Striatum Correlate with Cortical Cytoarchitectonic Organization in the Primate

We examined the striatal projections from different cytoarchitectonic regions of the insular cortex using anterograde and retrograde techniques. The shell and medial ventral striatum receive inputs primarily from the agranular and ventral dysgranular insula. The central ventral striatum receives inputs primarily from the dorsal agranular and dysgranular insula. Projections to the central ventral striatum originate from more posterior and dorsal insular regions than projections to the medial ventral striatum. The dorsolateral striatum receives projections primarily from the dorsal dysgranular and granular insula.

These results show that cytoarchitectonically less differentiated (agranular) insular regions project to the ventromedial "limbic" part of the ventral striatum, whereas more differentiated (granular) insular regions project to the dorsolateral "sensorimotor" part of the striatum. The finding that the ventral "limbic" striatum receives inputs from less differentiated regions of the insula is consistent with the general principle that less differentiated cortical regions project primarily to the "limbic" striatum. Functionally, the ventral striatum receives insular projections primarily related to integrating feeding behavior with rewards and memory, whereas the dorsolateral striatum receives insular inputs related to the somatosensation. Information regarding food acquisition in the insula may be sent to the intermediate area of the striatum.

Masanori Chikama, Nikolaus R. McFarland, David G. Amaral, and Suzanne N. Haber
Insular Cortical Projections to Functional Regions of the Striatum Correlate with Cortical Cytoarchitectonic Organization in the Primate
J. Neurosci. 17: 9686-9705; doi:

http://www.jneurosci.org/cgi/content/full/17/24/9686

Changes in brain activity related to eating chocolate

We performed successive H215O-PET scans on volunteers as they ate chocolate to beyond satiety. Thus, the sensory stimulus and act (eating) were held constant while the reward value of the chocolate and motivation of the subject to eat were manipulated by feeding. Non-specific effects of satiety (such as feelings of fullness and autonomic changes) were also present and probably contributed to the modulation of brain activity. After eating each piece of chocolate, subjects gave ratings of how pleasant/unpleasant the chocolate was and of how much they did or did not want another piece of chocolate. Regional cerebral blood flow was then regressed against subjects' ratings. Different groups of structures were recruited selectively depending on whether subjects were eating chocolate when they were highly motivated to eat and rated the chocolate as very pleasant [subcallosal region, caudomedial orbitofrontal cortex (OFC), insula/operculum, striatum and midbrain] or whether they ate chocolate despite being satiated (parahippocampal gyrus, caudolateral OFC and prefrontal regions). As predicted, modulation was observed in cortical chemosensory areas, including the insula and caudomedial and caudolateral OFC, suggesting that the reward value of food is represented here. Of particular interest, the medial and lateral caudal OFC showed opposite patterns of activity. This pattern of activity indicates that there may be a functional segregation of the neural representation of reward and punishment within this region. The only brain region that was active during both positive and negative compared with neutral conditions was the posterior cingulate cortex. Therefore, these results support the hypothesis that there are two separate motivational systems: one orchestrating approach and another avoidance behaviours.

Dana M. Small , Robert J. Zatorre , Alain Dagher , Alan C. Evans , and Marilyn Jones-Gotman
Changes in brain activity related to eating chocolate: From pleasure to aversion
Brain 124: 1720-1733.

http://brain.oxfordjournals.org/cgi/content/full/124/9/1720

A Specific Role for the Thalamus in Mediating the Interaction of Attention and Arousal in Humans

The physiological basis for the interaction of selective attention and arousal is not clearly understood. Here we present evidence in humans that specifically implicates the thalamus in this interaction. We used functional magnetic resonance imaging to measure brain activity during the performance of an attentional task under different levels of arousal. Activity evoked in the ventrolateral thalamus by the attentional task changed as a function of arousal. The highest level of attention-related thalamic activity is seen under conditions of low arousal (secondary to sleep deprivation) compared with high arousal (secondary to caffeine administration). Other brain regions were also active during the attentional task, but these areas did not change their activity as a function of arousal. Control experiments establish that this pattern of changes in thalamic activity cannot be accounted for by nonspecific effects of arousal on cerebral hemodynamics. We conclude that the thalamus is involved in mediating the interaction of attention and arousal in humans.

C. M. Portas, G. Rees, A. M. Howseman, O. Josephs, R. Turner, and C. D. Frith
A Specific Role for the Thalamus in Mediating the Interaction of Attention and Arousal in Humans
J. Neurosci. 18: 8979-8989; doi:

http://www.jneurosci.org/cgi/content/full/18/21/8979

The Connectional Organization of the Cortico-thalamic System of the Cat

Data on connections between the areas of the cerebral cortex and nuclei of the thalamus are too complicated to analyse with naked intuition. Indeed, the complexity of connection data is one of the major challenges facing neuroanatomy. Recently, systematic methods have been developed and applied to the analysis of the connectivity in the cerebral cortex. These approaches have shed light on the gross organization of the cortical network, have made it possible to test systematically theories of cortical organization, and have guided new electrophysiological studies. This paper extends the approach to investigate the organization of the entire corticothalamic network. An extensive collation of connection tracing studies revealed ~1500 extrinsic connections between the cortical areas and thalamic nuclei of the cat cerebral hemisphere. Around 850 connections linked 53 cortical areas with each other, and around 650 connections linked the cortical areas with 42 thalamic nuclei. Non-metric multidimensional scaling, optimal set analysis and non-parametric cluster analysis were used to study global connectivity and the `place' of individual structures within the overall scheme. Thalamic nuclei and cortical areas were in intimate connectional association. Connectivity defined four major thalamocortical systems. These included three broadly hierarchical sensory or sensory/motor systems (visual and auditory systems and a single system containing both somatosensory and motor structures). The highest stations of these sensory/motor systems were associated with a fourth processing system composed of prefrontal, cingulate, insular and parahippocampal cortex and associated thalamic nuclei (the `fronto-limbic system'). The association between fronto-limbic and somato-motor systems was particularly close.

J.W. Scannell , G.A.P.C. Burns , C.C. Hilgetag , M.A. O'Neil , and M.P. Young
The Connectional Organization of the Cortico-thalamic System of the Cat
Cereb. Cortex 9: 277-299.

http://cercor.oxfordjournals.org/cgi/content/full/9/3/277