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The olfactory thalamus: unanswered questions about the role of the mediodorsal thalamic nucleus in olfaction.

Courtiol E, Wilson DA - Front Neural Circuits (2015)

Bottom Line: In fact, anatomical evidence firmly demonstrates that the MDT receives direct input from primary olfactory areas including the piriform cortex and has dense reciprocal connections with the orbitofrontal cortex.However, many important questions regarding the MDT and olfaction remain unanswered.Our goal here is not only to briefly review the existing literature but also to highlight some of the remaining questions that need to be answered to better define the role(s) of the MDT in olfactory processing.

View Article: PubMed Central - PubMed

Affiliation: Emotional Brain Institute, Nathan Kline Institute for Psychiatric Research Orangeburg, NY, USA ; Department of Child and Adolescent Psychiatry, New York University Langone Medical Center NY, USA.

ABSTRACT
The mediodorsal thalamic nucleus (MDT) is a higher order thalamic nucleus and its role in cognition is increasingly well established. Interestingly, components of the MDT also have a somewhat unique sensory function as they link primary olfactory cortex to orbitofrontal associative cortex. In fact, anatomical evidence firmly demonstrates that the MDT receives direct input from primary olfactory areas including the piriform cortex and has dense reciprocal connections with the orbitofrontal cortex. The functions of this olfactory pathway have been poorly explored but lesion, imaging, and electrophysiological studies suggest that these connections may be involved in olfactory processing including odor perception, discrimination, learning, and attention. However, many important questions regarding the MDT and olfaction remain unanswered. Our goal here is not only to briefly review the existing literature but also to highlight some of the remaining questions that need to be answered to better define the role(s) of the MDT in olfactory processing.

No MeSH data available.


(A) Simplified schematic representation of the olfactory-related afferents and efferents of the mediodorsal thalamic nucleus (MDT) in rodents. Here we focused on the medial and central subnuclei of the MDT. Afferents in green and orange project mainly to the medial and central subnuclei of the MDT, respectively. Olfactory-related efferent projections of the MDT are outlined in pink (projection from MDT to endopiriform nucleus is represented with a dashed line because, to our knowledge, only one study has demonstrated this connection). LO and VO correspond to lateral and ventral orbital areas, respectively and AI to agranular insular areas. (B) Odor response in the MDT of urethane-anesthetized rats. (B1) Example of 3 odor responsive MDT units. From top to bottom: signal filtered between 300–3000Hz, raster plots of responses to the same odor presented three times and peristimulus time histograms (PSTH). Adapted from Courtiol and Wilson (2014). (B2) Example of odor-evoked local field potentials in the MDT. Top: local field potential filtered between 0.1–300 Hz and bottom: local field potential filtered in the beta band (15–35 Hz). Data used as an example here were described in Courtiol and Wilson (2014).
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Figure 1: (A) Simplified schematic representation of the olfactory-related afferents and efferents of the mediodorsal thalamic nucleus (MDT) in rodents. Here we focused on the medial and central subnuclei of the MDT. Afferents in green and orange project mainly to the medial and central subnuclei of the MDT, respectively. Olfactory-related efferent projections of the MDT are outlined in pink (projection from MDT to endopiriform nucleus is represented with a dashed line because, to our knowledge, only one study has demonstrated this connection). LO and VO correspond to lateral and ventral orbital areas, respectively and AI to agranular insular areas. (B) Odor response in the MDT of urethane-anesthetized rats. (B1) Example of 3 odor responsive MDT units. From top to bottom: signal filtered between 300–3000Hz, raster plots of responses to the same odor presented three times and peristimulus time histograms (PSTH). Adapted from Courtiol and Wilson (2014). (B2) Example of odor-evoked local field potentials in the MDT. Top: local field potential filtered between 0.1–300 Hz and bottom: local field potential filtered in the beta band (15–35 Hz). Data used as an example here were described in Courtiol and Wilson (2014).

Mentions: The thalamus is the major source of sensory information to the primary sensory cortex for all of the senses except olfaction. In fact, olfactory sensory neurons send their axons directly to the olfactory bulb which in turn projects to the primary olfactory cortex—a region including the piriform cortex, the anterior olfactory nucleus, the olfactory tubercle, the cortical nucleus of the amygdala, and the lateral entorhinal cortex (Price and Powell, 1971; Haberly and Price, 1977; Figure 1A). While there is no direct input from the olfactory sensory neurons to the thalamus, the MDT both receives and sends information to primary as well as secondary olfactory areas. An example of a major secondary olfactory area is the orbitofrontal cortex which has strong reciprocal connections with both the MDT and piriform cortex (Illig, 2005). While this review focuses on the MDT, the submedial nucleus of the thalamus also receives olfactory inputs (Price and Slotnick, 1983; Price, 1985).


The olfactory thalamus: unanswered questions about the role of the mediodorsal thalamic nucleus in olfaction.

Courtiol E, Wilson DA - Front Neural Circuits (2015)

(A) Simplified schematic representation of the olfactory-related afferents and efferents of the mediodorsal thalamic nucleus (MDT) in rodents. Here we focused on the medial and central subnuclei of the MDT. Afferents in green and orange project mainly to the medial and central subnuclei of the MDT, respectively. Olfactory-related efferent projections of the MDT are outlined in pink (projection from MDT to endopiriform nucleus is represented with a dashed line because, to our knowledge, only one study has demonstrated this connection). LO and VO correspond to lateral and ventral orbital areas, respectively and AI to agranular insular areas. (B) Odor response in the MDT of urethane-anesthetized rats. (B1) Example of 3 odor responsive MDT units. From top to bottom: signal filtered between 300–3000Hz, raster plots of responses to the same odor presented three times and peristimulus time histograms (PSTH). Adapted from Courtiol and Wilson (2014). (B2) Example of odor-evoked local field potentials in the MDT. Top: local field potential filtered between 0.1–300 Hz and bottom: local field potential filtered in the beta band (15–35 Hz). Data used as an example here were described in Courtiol and Wilson (2014).
© Copyright Policy
Related In: Results  -  Collection

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Figure 1: (A) Simplified schematic representation of the olfactory-related afferents and efferents of the mediodorsal thalamic nucleus (MDT) in rodents. Here we focused on the medial and central subnuclei of the MDT. Afferents in green and orange project mainly to the medial and central subnuclei of the MDT, respectively. Olfactory-related efferent projections of the MDT are outlined in pink (projection from MDT to endopiriform nucleus is represented with a dashed line because, to our knowledge, only one study has demonstrated this connection). LO and VO correspond to lateral and ventral orbital areas, respectively and AI to agranular insular areas. (B) Odor response in the MDT of urethane-anesthetized rats. (B1) Example of 3 odor responsive MDT units. From top to bottom: signal filtered between 300–3000Hz, raster plots of responses to the same odor presented three times and peristimulus time histograms (PSTH). Adapted from Courtiol and Wilson (2014). (B2) Example of odor-evoked local field potentials in the MDT. Top: local field potential filtered between 0.1–300 Hz and bottom: local field potential filtered in the beta band (15–35 Hz). Data used as an example here were described in Courtiol and Wilson (2014).
Mentions: The thalamus is the major source of sensory information to the primary sensory cortex for all of the senses except olfaction. In fact, olfactory sensory neurons send their axons directly to the olfactory bulb which in turn projects to the primary olfactory cortex—a region including the piriform cortex, the anterior olfactory nucleus, the olfactory tubercle, the cortical nucleus of the amygdala, and the lateral entorhinal cortex (Price and Powell, 1971; Haberly and Price, 1977; Figure 1A). While there is no direct input from the olfactory sensory neurons to the thalamus, the MDT both receives and sends information to primary as well as secondary olfactory areas. An example of a major secondary olfactory area is the orbitofrontal cortex which has strong reciprocal connections with both the MDT and piriform cortex (Illig, 2005). While this review focuses on the MDT, the submedial nucleus of the thalamus also receives olfactory inputs (Price and Slotnick, 1983; Price, 1985).

Bottom Line: In fact, anatomical evidence firmly demonstrates that the MDT receives direct input from primary olfactory areas including the piriform cortex and has dense reciprocal connections with the orbitofrontal cortex.However, many important questions regarding the MDT and olfaction remain unanswered.Our goal here is not only to briefly review the existing literature but also to highlight some of the remaining questions that need to be answered to better define the role(s) of the MDT in olfactory processing.

View Article: PubMed Central - PubMed

Affiliation: Emotional Brain Institute, Nathan Kline Institute for Psychiatric Research Orangeburg, NY, USA ; Department of Child and Adolescent Psychiatry, New York University Langone Medical Center NY, USA.

ABSTRACT
The mediodorsal thalamic nucleus (MDT) is a higher order thalamic nucleus and its role in cognition is increasingly well established. Interestingly, components of the MDT also have a somewhat unique sensory function as they link primary olfactory cortex to orbitofrontal associative cortex. In fact, anatomical evidence firmly demonstrates that the MDT receives direct input from primary olfactory areas including the piriform cortex and has dense reciprocal connections with the orbitofrontal cortex. The functions of this olfactory pathway have been poorly explored but lesion, imaging, and electrophysiological studies suggest that these connections may be involved in olfactory processing including odor perception, discrimination, learning, and attention. However, many important questions regarding the MDT and olfaction remain unanswered. Our goal here is not only to briefly review the existing literature but also to highlight some of the remaining questions that need to be answered to better define the role(s) of the MDT in olfactory processing.

No MeSH data available.