혼자 공부하면서 생각한 것들을 적어가는 공간입니다.
의견 주고받으면서 같이 공부하실 분은 환영입니다.
Cochlear neural degeneration disrupts hearing in background noise by increasing auditory cortex internal noise
Jennifer Resnik1, Daniel B Polley2
PMID: 33561398 DOI: 10.1016/j.neuron.2021.01.015
Abstract
Correlational evidence in humans suggests that selective difficulties hearing in noisy, social settings may reflect premature auditory nerve degeneration. Here, we induced primary cochlear neural degeneration (CND) in adult mice and found direct behavioral evidence for selective detection deficits in background noise. To identify central determinants for this perceptual disorder, we tracked daily changes in ensembles of layer 2/3 auditory cortex parvalbumin-expressing inhibitory neurons and excitatory pyramidal neurons with chronic two-photon calcium imaging. CND induced distinct forms of plasticity in cortical excitatory and inhibitory neurons that culminated in net hyperactivity, increased neural gain, and reduced adaptation to background noise. Ensemble activity measured while mice detected targets in noise could accurately decode whether individual behavioral trials were hits or misses. After CND, random surges of hypercorrelated cortical activity occurring just before target onset reliably predicted impending detection failures, revealing a source of internal cortical noise underlying perceptual difficulties in external noise.
청각(Hearing)은 우리가 갖고 있는 오감(Vision, Hearing, Taste, Touch, Smell) 중 하나이며, 굉장히 독특한 특징 몇 가지를 갖고 있다. 그중 하나가 'Cocktail party effect (칵테일파티 효과)'인데, 이는 시끄러운 주변 소음이 있는 환경에 노출이 된 상태임에도 대화 상대의 말에 집중, 청각자극을 선택적으로 받아들이는 현상을 말한다. 단순히 '청각(auditory)' 뿐만 아니라 '집중(attention)'이라는 요소도 고려해야 하지만, 주변의 소음으로부터 원하는 input을 분리해 내는 것은 대단한 능력인 것 같다. 필자가 알고 있는 내에서, '칵테일파티 효과'가 어떤 원리인지 - 우리의 뇌가 주변 잡음을 어떻게 인식하는지, 잡음을 어떻게 제거하고 원하는 소리에 집중을 할 수 있는지, 이 과정에서 뇌의 어떤 영역이 중요한지 - 아직 정확히 알려지지 않은 걸로 알고 있다. 조금 더 내용을 확장하면, 우리가 많이 사용하고 있는 이어폰, 그리고 이어폰에 의한 청각 손상, 노이즈 캔슬링, 이 모든 것들이 다 밀접하게 연관된 주제가 될 것 같다. 특히, 미래에는 노화로 인한 청각 손상보다 이어폰을 통한 손상이나 외부 자극에 의한 손상이 점점 비중이 커질 수 있는데, 이러한 관점에서 이 논문의 결과는 매우 흥미로운 것 같다.
한 줄로 후려쳐서 요약하면, Top-down network-level change of auditory cortical activity induced impairment in sound perception in a noisy environment.
Figure 1: Experiment setup
- a: Cochlear neural degeneration by ouabian injection (Selective elimination of type 1 spiral ganglion neurons (SGNs; afferent nerve fibers)
- b: Example ABR results
- c: ABR wave 1 amp from both CND/Control groups, before/after.
- d: ABR threshold shift results
- e: DPOAE results
- f: Experiment schedule/paradigm: Since it is a detection task, they used one cue with different tone levels.
- g: Psychometric curves from CND/Control groups. In noise condition, effects of CND appeared.
- h: Summarized behavior results.
Figure 2: Dichotomy of pyramidal neurons' activity and PV neurons' activity
- a: cartoon
- b: another cartoon, imaging scheme (Recording of both pyramidal & PV neurons)
- c: Longitudinal recording
- d: Spontaneous activity of 6 pyramidal neurons and 2 PV neurons. It is unclear to me since they used 'deconvolved' spontaneous activity traces. What is the meaning of 1 event? The vertical scale bar denotes 50 events per second, and it is definitely hard to interpret: (According to the graph, are those neurons with 20~30 hz activity? How come pyramidal neurons produce more spikes than PV neurons?).
- e: Pre three days baselined z-score delta-spontaneous activity. Only CND groups show strong dynamics.
- f: Dichotomy of two population's activity. So, aren't they tightly connected even in the baseline? Or the connectivity just changed after the CND?
- g: Asymmetry index
Figure 3: Sound evoked activity from quiet/noise environment
- a: Pyramidal in quiet
- b: Pyramidal in noise
- c: PV in quiet
- d: PV in noise
- e: behavior impairment in the noise condition
- f, g: Averaged sound-evoked activities from both pyramidal and PV neurons. It is Z-socred relative to the pre-stimulus spontaneous activity, so that is why CND-PV shows a lower value (due to high spontaneous activity level).
Figure 4: Decoding of sound response
- a, d: Single neuron, single trial level PSTH heat map. Hyper activity of pyramidal neurons before cue onset. The phenomenone became more significant in noisy environmentsingle neuron, single-trial level PSTH heat map. The hyperactivity of pyramidal neurons before cue onset. The phenomenon became more significant in a noisy environment.
-b, e: Ensemble activities onto a PC plane(PC1 vs. PC2). Decoding accuracy got lower after CND but eventually became to the similar level in quiet environment. However, in a noise environment, it failed to recover.
Figure 5: Ensemble dynamic during behavior (Hit vs. Miss)
- a: Methods
- b: Experiment design
- c: In the noise environment, miss trials had pre-stim increased activity.
Figure 6: Decoding of behavior performance
- a, c: Averaged activity of the pyramidal neurons in a quiet-/noisy-environment. In the noise environment, pyramidal neruons showed increased activity before the sound onset.
- b, d: Only after-CND condition showed decreased decoding accuraty.
Figure 7: Increased cross-correlation between neurons during miss trials
- a: Imaged plane
- b: Deconvolved activity. Slight increased activity in After-CND miss trials.
- c: Example cross-correlation during hit trials and miss trials.
- d, e: Averaged cross-correlation between pyramidal neurons and PV neurons and their histograms.
- f: Cross-correlation areas from each condition.
- g: Distinct neural activity in neuropathic mice during the pre-target noise period.
