Alexander N.J. Pietersen

Transition between fast and slow gamma modes in rat hippocampus area CA1 in vitro is modulated by slow CA3 gamma oscillations

The synchronisation of neuronal activity at gamma frequencies (30–100 Hz) could determine the effectiveness of neuronal communication. Gamma oscillations in the CA1 region of the hippocampus in vitro was thought to be dependent on gamma oscillations generated in area CA3, but in vivo CA1 can generate gamma oscillations independently. In this study we found that activating acetylcholine receptors induced stable gamma oscillations in the CA1 local network isolated in slices in vitro that were faster than those in CA3, but relied on similar neuronal circuitry involving feedback inhibition. Gamma frequency inputs from CA3 (spontaneous in intact hippocampal slices or stimulated in isolated CA1) can suppress the local fast gamma oscillation in CA1 and force it to adopt the slower CA3 oscillation through feed‐forward inhibition. This modulation could allow CA1 to alternate between effective communication with the entorhinal cortex and CA3, which may regulate memory encoding and memory recall phases.

Colour and pattern selectivity of receptive fields in superior colliculus of marmoset monkeys.

•  In addition to supplying signals for conscious visual perception, the pathways from eye to brain serve visual functions such as reflex eye movements, which are controlled by a brain area called the superior colliculus (SC). •  It is known that short‐wavelength sensitive (S or ‘blue’) cone photoreceptors serve an evolutionary ancient pathway for colour vision but whether S cones also contribute to reflex eye movements is poorly understood. •  We show that in recordings from anaesthetised marmoset monkeys, S cones do not contribute to visual responses in the SC. Thus, although S cones are a primitive part of the visual system their signals are selectively directed to thalamo‐cortical pathways serving colour vision. •  The result also implies that colour‐selective responses reported in SC of awake monkeys must arrive through indirect (non‐retinal) inputs to the SC.

Emergence of Complex Wave Patterns in Primate Cerebral Cortex

Slow brain rhythms are attributed to near-simultaneous (synchronous) changes in activity in neuron populations in the brain. Because they are slow and widespread, synchronous rhythms have not been considered crucial for information processing in the waking state. Here we adapted methods from turbulence physics to analyze δ-band (1–4 Hz) rhythms in local field potential (LFP) activity, in multielectrode recordings from cerebral cortex in anesthetized marmoset monkeys. We found that synchrony contributes only a small fraction (less than one-fourth) to the local spatiotemporal structure of δ-band signals. Rather, δ-band activity is dominated by propagating plane waves and spatiotemporal structures, which we call complex waves. Complex waves are manifest at submillimeter spatial scales, and millisecond-range temporal scales. We show that complex waves can be characterized by their relation to phase singularities within local nerve cell networks. We validate the biological relevance of complex waves by showing that nerve cell spike rates are higher in presence of complex waves than in the presence of synchrony and that there are nonrandom patterns of evolution from one type of complex wave to another. We conclude that slow brain rhythms predominantly indicate spatiotemporally organized activity in local nerve cell circuits, not synchronous activity within and across brain regions.

Relationship between cortical state and spiking activity in lateral geniculate nucleus of anaesthetised marmosets

How parallel are the primate visual pathways? In the present study, we demonstrate that parallel visual pathways in the dorsal lateral geniculate nucleus (LGN) show distinct patterns of interaction with rhythmic activity in the primary visual cortex (V1). In the V1 of anaesthetized marmosets, the EEG frequency spectrum undergoes transient changes that are characterized by fluctuations in delta‐band EEG power. We show that, on multisecond timescales, spiking activity in an evolutionary primitive (koniocellular) LGN pathway is specifically linked to these slow EEG spectrum changes. By contrast, on subsecond (delta frequency) timescales, cortical oscillations can entrain spiking activity throughout the entire LGN. Our results are consistent with the hypothesis that, in waking animals, the koniocellular pathway selectively participates in brain circuits controlling vigilance and attention.

Relationship between cortical state and spiking activity in the lateral geniculate nucleus of marmosets

How parallel are the primate visual pathways? In the present study, we demonstrate that parallel visual pathways in the dorsal lateral geniculate nucleus (LGN) show distinct patterns of interaction with rhythmic activity in the primary visual cortex (V1). In the V1 of anaesthetized marmosets, the EEG frequency spectrum undergoes transient changes that are characterized by fluctuations in delta‐band EEG power. We show that, on multisecond timescales, spiking activity in an evolutionary primitive (koniocellular) LGN pathway is specifically linked to these slow EEG spectrum changes. By contrast, on subsecond (delta frequency) timescales, cortical oscillations can entrain spiking activity throughout the entire LGN. Our results are consistent with the hypothesis that, in waking animals, the koniocellular pathway selectively participates in brain circuits controlling vigilance and attention.

Chromatic summation and receptive field properties of blue-on and blue-off cells in marmoset lateral geniculate nucleus

Graphical abstract Figure. No Caption available. HighlightsBlue‐on and blue‐off receptive‐field properties were identified in primate LGN.Sensitivities to short‐wave (S) and medium/long‐wave (ML) cone contrast are similar.S and ML receptive field subunits have similar spatial extents.Vector sum model predicts responses to achromatic S + ML and chromatic S − ML contrast.Blue‐on and blue‐off receptive fields select more for chromatic than spatial contrast. Abstract The “blue‐on” and “blue‐off” receptive fields in retina and dorsal lateral geniculate nucleus (LGN) of diurnal primates combine signals from short‐wavelength sensitive (S) cone photoreceptors with signals from medium/long wavelength sensitive (ML) photoreceptors. Three questions about this combination remain unresolved. Firstly, is the combination of S and ML signals in these cells linear or non‐linear? Secondly, how does the timing of S and ML inputs to these cells influence their responses? Thirdly, is there spatial antagonism within S and ML subunits of the receptive field of these cells? We measured contrast sensitivity and spatial frequency tuning for four types of drifting sine gratings: S cone isolating, ML cone isolating, achromatic (S + ML), and counterphase chromatic (S − ML), in extracellular recordings from LGN of marmoset monkeys. We found that responses to stimuli which modulate both S and ML cones are well predicted by a linear sum of S and ML signals, followed by a saturating contrast‐response relation. Differences in sensitivity and timing (i.e. vector combination) between S and ML inputs are needed to explain the amplitude and phase of responses to achromatic (S + ML) and counterphase chromatic (S − ML) stimuli. Best‐fit spatial receptive fields for S and/or ML subunits in most cells (>80%) required antagonistic surrounds, usually in the S subunit. The surrounds were however generally weak and had little influence on spatial tuning. The sensitivity and size of S and ML subunits were correlated on a cell‐by‐cell basis, adding to evidence that blue‐on and blue‐off receptive fields are specialised to signal chromatic but not spatial contrast.