Recent replies to "JOURNAL CLUB: Giving Sounds the Silent Treatment"

Reply from Alfredo Pereira Jr

Alfredo Pereira Jr — Sun, 20 Apr 2008 10:31:49 -0000

Dear Lizzie:

The reported research and your comments are very good. The question that I raise is a bit different from your discussion questions.
I used to think that sparse coding occurs mainly at associative areas, where stimuli objects and events are recognized as a whole (e.g. recognition of faces in temporal cortex). Primary sensory processing is usually thought as being non selective.
The picture that I have is of a pyramid, where the base corresponds to primary sensory processing, with massive activation depending only on receptive fields properties, and the top is the “grandmother cell” or sparse group of neurons who have the final word about the identity of the stimulus being recognized.
Therefore, I conclude that the results of the experiment “must” involve the effect of attention. The rodents were probably not interested in these sounds. I also suspect that rodent orientation is far more dependent on other sensory modalities.

Best

Alfredo Pereira Jr.

Reply from Alfredo Pereira Jr

Alfredo Pereira Jr — Wed, 16 Apr 2008 14:44:30 -0000

Dear Noah,

Many thanks for the clarification. My confusion came from the phrase “they presented each neuron with identical sound repertoires (tones, sweeps, white-noise bursts, and natural sounds)”. I would be delighted to know that neurons respond directly to these sounds! Sorry for my mistake.

Best

Alfredo

Reply from Noah Gray

Noah Gray — Tue, 15 Apr 2008 19:36:15 -0000

Alfredo, if I understand your question correctly, there was no bypass. The sensory system was entirely intact, so sound presentation caused normal circuit activation, eliciting the release of transmitter from an upstream connection, producing a spike in the postsynaptic, recorded neuron. The identity of the presynaptic partner depends on the depth of the recording, since different cortical layers receive different projections.

Reply from Alfredo Pereira Jr

Alfredo Pereira Jr — Tue, 15 Apr 2008 19:19:56 -0000

Dear Lizzie:

I need a clarification. In natural conditions, cortical neurons do not respond to sounds, but to biological signals (mostly transmitters) that “carry” sensory patterns. The binding of neurotransmitter and membrane receptor is ruled by a molecular “input code”. How was this code bypassed in the experiment?

Thanks!

Best Regards

Alfredo Pereira Jr.