Multisensory convergence
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Multisensory convergence. Traditionally, represented by inputs from more than one sensory modality , each of which can independently activate the target neuron. (50 yr)

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Multisensory convergence

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Multisensory convergence

Multisensory convergence

  • Traditionally, represented by inputs from more than one sensory modality, each of which can independently activate the target neuron. (50 yr)

  • Recently, multisensory neuron excited to suprathreshold levels by only one sensory modality, yet inputs from a second modality can significantly modulate these responses through facilitation or suppression (25 yr)

    Subthreshold multisensory effects may be a general feature


Cat auditory cortex and faes

Cat Auditory Cortex and FAES


Auditory field of the anterior ectosylvian sulcus faes

Auditory field of the anterior ectosylvian sulcus (FAES)

  • Prefer complex sounds /c multiple frequencies & sensitivity to sound location

  • Reversible deactivation of leads to deficits in sound localization

  • Bimodal neurons identified largely along shared borders

  • Nonbimodal forms of multisensory processing in visual and somatosensory cortices. Allman 2007

Somatosensory: SIV

Visual: anterior ectosylvian visual (AEV)

Courtesy of Stein 2008


Hypothesis

Hypothesis

  • Subthreshold-processing patterns might be ubiquitous to multisensory systems

  • Multisensory processing is subserved by not just bimodal neurons, but by a range of multisensory convergence patterns.


Methods

Methods

  • Craniotomy to expose auditory cortex (deep anesth. pentobarbital)

  • a glass-insulated tungsten electrode was inserted vertically and advanced into the FAES (shallow anesth. with ketamine + acepromazine, still some reflex kept)

  • Visual cues: moving light or dark bars projected onto a translucent hemisphere

  • Auditory cues: clicks, claps, whistles, & hisses

  • Somatosensory stimuli: air puffs, brushes, taps to the body surface, as well as compression of deep tissues and joint rotation.


Faes the sensory responses

FAES & the sensory responses

Auditory neurons: 70% (135/193)

Visual: 13.5% (26/193) ventrally (AEV)

A+V (bimodal): 14.5% (28/193)

2% unresponsive

No other sensory convergence (v+s)

FAES+AEV

Bimodal: neurons response independently

to separate visual and auditory stimulation

Subthreshold multisensory neurons: response to only one modality but influenced by other modality


Response of faes neurons to auditory visual and combined auditory visual stimulation

Response of FAES neurons to auditory, visual, and combined auditory–visual stimulation

16.5% of all neurons

Within FAES


Multisensory influences on auditory processing in faes

Multisensory influences on auditory processing in FAES

MS: multisensory, bimodal & subthreshold


Conclusion

Conclusion

  • Neurons in auditory FAES exhibit both bimodal and subthreshold forms of multisensory convergence and processing.

  • Subthreshold multisensory neurons produce response levels intermediate to those elicited in bimodal (multisensory convergence) or in unimodal neurons (no convergence).


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