Biology subjects

Hamersky, G. R.

Publications and source records attributed to Hamersky, G. R..

3 recordsLinked to original sources

bioRxiv2023

Unexpected suppression of neural responses to natural foreground versus background sounds in auditory cortex

In everyday hearing, listeners encounter complex auditory scenes containing overlapping sounds that must be grouped into meaningful sources, or streamed, to be perceived accurately. A common example of this problem is the perception of a behaviorally relevant foreground stimulus (speech, vocalizations) in complex background noise (environmental, machine noise). Studies using a foreground/background contrast have shown that high-order areas of auditory cortex in humans pre-attentively form an enhanced representation of the foreground over background stimulus. Achieving this invariant foreground representation requires identifying and grouping the features that comprise the background noise so that they can be removed from the representation of the foreground. To study the cortical computations underlying representation of concurrent background (BG) and foreground (FG) stimuli, we recorded single unit responses in the auditory cortex (AC) of ferrets during presentation of natural sound excerpts from these two categories. In primary and secondary AC, we found overall suppression of responses when BGs and FGs were presented concurrently relative to the sum of responses to the same stimuli in isolation. Surprisingly, and in contrast to percepts that emphasize dynamic FGs, responses to FG sounds were suppressed relative to the paired BG sound. The degree of relative FG suppression could be explained by spectro-temporal statistics unique to each natural sound. Moreover, systematic degradation of the same spectro-temporal features decreased FG suppression as the sound categories became progressively less statistically distinct. The strongly suppressed representation of FG sounds in single units of AC in the presence of BG sound reveals a novel insight into how complex acoustic scenes are encoded at early stages of auditory processing.

neuroscience↗

bioRxiv2023

Task-specific invariant representation in auditory cortex

Categorical sensory representations are critical for many behaviors, including speech perception. In the auditory system, categorical information is thought to arise hierarchically, becoming increasingly prominent in higher order cortical regions. The neural mechanisms that support this robust and flexible computation remain poorly understood. Here, we studied sound representations in primary and non-primary auditory cortex while animals engaged in a challenging sound discrimination task. Population-level decoding of simultaneously recorded single neurons revealed that task engagement caused categorical sound representations to emerge in non-primary auditory cortex. In primary auditory cortex, task engagement caused a general enhancement of sound decoding that was not specific to task-relevant categories. These findings are consistent with mixed selectivity models of neural disentanglement, in which early sensory regions build an overcomplete representation of the world and allow neurons in downstream brain regions to flexibly and selectively read out behaviorally relevant, categorical information.

neuroscience↗

bioRxiv2018

Dissecting transcriptomic signatures of neuronal differentiation and maturation using iPSCs

Human induced pluripotent stem cells (hiPSCs) are a powerful model of neural differentiation and maturation. We present a hiPSC transcriptomics resource on corticogenesis from 5 iPSC donor and 13 subclonal lines across nine time points over 5 broad conditions: self-renewal, early neuronal differentiation, neural precursor cells (NPCs), assembled rosettes, and differentiated neuronal cells that were validated using electrophysiology. We identified widespread changes in the expression of individual transcript features and their splice variants, gene networks, and global patterns of transcription. We next demonstrated that co-culturing human NPCs with rodent astrocytes resulted in mutually synergistic maturation, and that cell type-specific expression data can be extracted using only sequencing read alignments without potentially disruptive cell sorting. We lastly developed and validated a computational tool to estimate the relative neuronal maturity of iPSC-derived neuronal cultures and human brain tissue, which were maturationally heterogeneous but contained subsets of cells most akin to adult human neurons.

genomics↗