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

  • 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


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

  • 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

  • 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

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

16.5% of all neurons

Within FAES


Multisensory influences on auditory processing in FAES

MS: multisensory, bimodal & subthreshold


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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