Characterization of extracellular spike waveforms recorded in wallaby primary visual cortex
Young Jun Jung1,2,3, Shi H Sun2, Ali Almasi2
1Department of Biomedical Engineering, The University of Melbourne, Melbourne, VIC, Australia.
Insights
Researchers studied visual cortex neurons in Tammar wallabies, finding diverse spiking patterns and receptive field properties. Results suggest a higher degree of orientation selectivity in the wallaby lateral geniculate nucleus than previously thought.
Area of Science:
- Neuroscience
- Visual Processing
- Comparative Anatomy
Background:
- The primary visual cortex (V1) processes visual information.
- Understanding neuronal properties in different species aids in understanding visual system evolution.
- Tammar wallabies are highly visual marsupials, making them a unique model for visual cortex studies.
Purpose of the Study:
- To characterize receptive field (RF) properties and correlate them with spike shapes in the Tammar wallaby's primary visual cortex (V1).
- To investigate the prevalence of different neuronal firing patterns (spiking types) in the wallaby cortex.
- To infer potential origins of different neuronal populations and their functional properties, including orientation selectivity.
Main Methods:
- Extracellular recordings from 642 units in the Tammar wallaby V1.
- Objective estimation of receptive field (RF) characteristics using the non-linear input model (NIM).
- Correlation of RF properties with neuronal spike shapes.
Main Results:
- Wallaby cortical units showed a dominance of regular spiking (RS) at 68%, followed by fast spiking (FS) at 12%.
- A significant portion (47%) of positive spiking (PS) units were non-orientation selective with linear RFs, suggesting potential LGN origins.
- Most FS and RS cells (70-80%) exhibited orientation-selective RFs, with a mix of linear and nonlinear properties.
Conclusions:
- The diverse spiking patterns in wallaby V1 suggest a mix of neuronal types, with RS likely representing pyramidal or spiny stellate cells.
- The high proportion of orientation-selective neurons in the wallaby LGN is implied by the properties of PS units.
- Further research is needed to clarify the cellular origins of triphasic spiking (TS) and compound spiking (CS) units.
Abstract:
Extracellular recordings were made from 642 units in the primary visual cortex (V1) of a highly visual marsupial, the Tammar wallaby. The receptive field (RF) characteristics of the cells were objectively estimated using the non-linear input model (NIM), and these were correlated with spike shapes. We found that wallaby cortical units had 68% regular spiking (RS), 12% fast spiking (FS), 4% triphasic spiking (TS), 5% compound spiking (CS) and 11% positive spiking (PS). RS waveforms are most often associated with recordings from pyramidal or spiny stellate cell bodies, suggesting that recordings from these cell types dominate in the wallaby cortex. In wallaby, 70-80% of FS and RS cells had orientation selective RFs and had evenly distributed linear and nonlinear RFs. We found that 47% of wallaby PS units were non-orientation selective and they were dominated by linear RFs. Previous studies suggest that the PS units represent recordings from the axon terminals of non-orientation selective cells originating in the lateral geniculate nucleus (LGN). If this is also true in wallaby, as strongly suggested by their low response latencies and bursty spiking properties, the results suggest that significantly more neurons in wallaby LGN are already orientation selective. In wallaby, less than 10% of recorded spikes had triphasic (TS) or sluggish compound spiking (CS) waveforms. These units had a mixture of orientation selective and non-oriented properties, and their cellular origins remain difficult to classify.
