Biology subjects

Alitto, H. J.

Publications and source records attributed to Alitto, H. J..

4 recordsLinked to original sources

bioRxiv2025

Causal role for pulvinar burst firing in thalamo-cortical attention control

The primate pulvinar has been implicated in coordinating cortical networks during attention, but its causal role remains elusive. Like other thalamic nuclei, pulvinar neurons switch between tonic and burst firing, but whether bursts influence behavior and cognitive processes is unknown. Here, we show that pulvinar bursts are not only modulated by attention but also predict behavioral performance. In macaques performing a covert attention task, bursts were more frequent for non-cued targets and uniquely reconfigured population codes in parietal cortex. Crucially, electrical microstimulation of pulvinar triggered bursts that enhanced target detection and synchronized cortical spiking, with behavioral benefits scaling with the strength of burst recruitment. These results establish pulvinar bursts as a causal driver of attention, revealing a thalamo-cortical mechanism by which thalamus exerts moment-to-moment control over cortical processing and behavior.

animal behavior and cognition↗

bioRxiv2025

Dynamic Modulation of Beta-Band Oscillations in the LGN and Their Role in Visual Processing

Neuronal oscillations are a ubiquitous feature of thalamocortical networks and can be dynamically modulated across processing states, enabling thalamocortical communication to flexibly adapt to varying environmental and behavioral demands. The lateral geniculate nucleus (LGN), like all thalamic nuclei, engages in reciprocal synaptic interactions with the cortex, relaying retinal information to and receiving feedback input from primary visual cortex (V1). While retinal excitation is the primary driver of LGN activity, retinal synapses represent a minority of the total synaptic input onto LGN neurons, allowing for both retinogeniculate and geniculocortical signals to be influenced by nonretinal sources. To gain a holistic view of network processing in the geniculocortical pathway, we performed simultaneous extracellular recordings from the LGN and V1 of behaving macaque monkeys, measuring local field potentials (LFPs) and spiking activity. These recordings revealed prominent beta-band oscillations coherent between the LGN and V1 that influenced spike timing in the LGN and were statistically consistent with a feedforward process from the LGN to V1. These thalamocortical oscillations were suppressed by visual stimulation, spatial attention, and behavioral arousal, strongly suggesting that these oscillations are not a feature of active visual processing. Instead, they appear analogous to occipital lobe, alpha oscillations recorded in humans and may represent a signature of signal suppression that occurs during periods of low engagement or active distractor suppression. Significance StatementOscillations within thalamocortical networks in the awake state are generally believed to enhance communication between the thalamus and cortex, allowing circuits to flexibly respond to changes in sensory, behavioral, and cognitive demands. Here, we show that oscillations within and between the LGN and V1 are suppressed by increases in visual stimulation, increases in behavioral arousal, and shifts in covert spatial attention. We therefore conclude that these oscillations are not a mechanism to enhance the transmission of retinal information through the LGN to V1. Instead, we propose that they are a signature of signal suppression that occurs when network engagement is low or during active distractor suppression.

neuroscience↗

bioRxiv2025

Spatial Attention Weakly Modulates Visual Responses in the Lateral Geniculate Nucleus

Visual responses in the cerebral cortex are strongly influenced by shifts in spatial attention. This modulation of visual processing includes changes in firing rate, decreased response variability, and decreased interneuronal correlations; all of which are thought to underlie enhanced visual perception near the center of attention at the cost of visual perception at other locations. Visual information from the retina is relayed to primary visual cortex via neurons in the lateral geniculate nucleus (LGN) of the dorsal thalamus. Although early studies describe an enhancement of LGN activity with spatial attention, more recent work has cast doubt on this view. Given its strategic position as the gateway to the cortex, an understanding of the effects of attention on visual processing in the LGN is important. We therefore performed experiments to reexamine the influence of covert spatial attention on the spiking activity of single units in the macaque LGN and applied a broad set of analyses and functional metrics to assess possible effects. Our results reveal a statistically significant effect of spatial attention in the LGN: firing rates were slightly higher and more reliable when monkeys directed attention towards the receptive fields of recorded neurons compared to when attention was directed to different retinotopic locations. However, effects were much smaller than previously reported ([~]1% vs [~]4%) and further analyses suggest that effects are weak and inconsistent. Thus, while spatial attention does exert an influence in the LGN, its effects are weak and may have limited impact on downstream processing. Significance StatementThe lateral geniculate nucleus (LGN) is a critical relay in the visual system, shaping the flow of sensory information from the eye to the brain. Although higher-order brain regions show strong modulation by attention, it remains unclear whether the LGN is similarly affected. By directly recording LGN activity in monkeys performing a covert attention task, we found that spatial attention produces only weak and inconsistent modulation of visual responses. These findings suggest that the LGN largely operates independently of spatial attention, highlighting a potential boundary between early sensory processing and cognitive control.

neuroscience↗

bioRxiv2018

The augmentation of retinogeniculate communication during thalamic burst mode

Retinal signals are transmitted to cortex via neurons in the lateral geniculate nucleus (LGN), where they are processed in burst or tonic response mode. Burst mode occurs when LGN neurons are sufficiently hyperpolarized for T-Type Ca2+ channels to de-inactivate, allowing them to open in response to a depolarization which can trigger a high-frequency sequence of Na+-based spikes (i.e. burst). In contrast, T-type channels are inactivated during tonic mode and do not contribute to spiking. Although burst mode is commonly associated with sleep and the disruption of retinogeniculate communication, bursts can also be triggered by visual stimulation, thereby transforming the retinal signals relayed to the cortex.\n\nTo determine how burst mode affects retinogeniculate communication, we made recordings from monosynaptically connected retinal ganglion cells and LGN neurons in the cat during visual stimulation. Our results reveal a robust augmentation of retinal signals within the LGN during burst mode. Specifically, retinal spikes were more effective and often triggered multiple LGN spikes during periods likely to have increased T-Type Ca2+ activity. Consistent with the biophysical properties of T-Type Ca2+ channels, analysis revealed that effect magnitude was correlated with the duration of the preceding thalamic interspike interval and occurred even in the absence of classically defined bursts. Importantly, the augmentation of geniculate responses to retinal input was not associated with a degradation of visual signals. Together, these results indicate a graded nature of response mode and suggest that, under certain conditions, bursts facilitate the transmission of visual information to the cortex by amplifying retinal signals.\n\nSignificanceThe thalamus is the gateway for retinal information traveling to the cortex. The lateral geniculate nucleus (LGN), like all thalamic nuclei, has two classically defined categories of spikes--tonic and burst--that differ in their underlying cellular mechanisms. Here we compare retinogeniculate communication during burst and tonic response modes. Our results show that retinogeniculate communication is enhanced during burst mode and visually evoked thalamic bursts, thereby augmenting retinal signals transmitted to cortex. Further, our results demonstrate that the influence of burst mode on retinogeniculate communication is graded and can be measured even in the absence of classically defined thalamic bursts.

neuroscience↗