Stay tuned for more (or less): Neural selectivity and perception of numerosity and other quantities

In our daily lives, we have to process information about all kinds of quantities such as the set size of a group of items (i.e., numerosity), time and size, among others. We have previously reported specialized neurons in our brain which respond selectively to or ‘prefer’ a specific number of items such as one, two or three. These neurons are organized topographically which means that these neurons are laid out in a shape that allows those most closely related to communicate and interact over the shortest possible distance in the brain. The general research goal of this thesis was to examine the properties of numerosity-tuned neural populations, and numerosity perception as part of a generalized quantity system by investigating the possibility of shared, tuned mechanisms between numerosity and time, and other quantities and sensory modalities. We first examined whether and how the selective response or preference of these numerosity selective neurons can change based on recent sensory experience. We used the method of adaptation and ultra-high-field 7 Tesla fMRI, where participants were repeatedly shown a low or high numerosity so to adapt the numerosity-selective neural populations. Sensory adaptation, makes the appearance of subsequently presented stimuli appear more different from the adapting stimulus than they actually are. This method is a powerful tool which allows us to make inferences about the existence of specialized neurons in the brain which respond selectively to the adapting stimuli. We show the dynamic nature of numerosity selective neural populations, where neural numerosity selectivity was altered systematically in all numerosity selective brain areas. Based on findings showing brain regions which process more than one type of quantity, such as numerosity and time, we proceeded to use cross-adaptation to numerosity and time to study whether neural populations selective for numerosity or time interact. We found an unbalanced interaction between numerosity and time where adaptation to time affected numerosity perception but not the other way around. After finding this interaction between neurons selective for processing numerosity and time, further experiments showed that the neural populations underlying the effect of adaptation to time on numerosity perception are partially distinct from those underlying the effect of the time of adaptation on numerosity perception. Collectively, these results highlight that there are partially overlapping neural mechanisms which are dedicated for processing both numerosity and time. We propose that neurons which are selective or are ‘tuned’ to different quantities such as number, time or size are fundamental to understanding quantity perception. We illustrate how the properties of quantity-tuned neurons can underlie various perceptual phenomena. We further show that quantity-tuned neurons are organized in distinct but overlapping neural networks. We suggest that this overlap in tuning provides the neural basis for perceptual interactions between different quantities

Stay tuned for more (or less): Neural selectivity and perception of numerosity and other quantities

In our daily lives, we have to process information about all kinds of quantities such as the set size of a group of items (i.e., numerosity), time and size, among others. We have previously reported specialized neurons in our brain which respond selectively to or ‘prefer’ a specific number of items such as one, two or three. These neurons are organized topographically which means that these neurons are laid out in a shape that allows those most closely related to communicate and interact over the shortest possible distance in the brain. The general research goal of this thesis was to examine the properties of numerosity-tuned neural populations, and numerosity perception as part of a generalized quantity system by investigating the possibility of shared, tuned mechanisms between numerosity and time, and other quantities and sensory modalities. We first examined whether and how the selective response or preference of these numerosity selective neurons can change based on recent sensory experience. We used the method of adaptation and ultra-high-field 7 Tesla fMRI, where participants were repeatedly shown a low or high numerosity so to adapt the numerosity-selective neural populations. Sensory adaptation, makes the appearance of subsequently presented stimuli appear more different from the adapting stimulus than they actually are. This method is a powerful tool which allows us to make inferences about the existence of specialized neurons in the brain which respond selectively to the adapting stimuli. We show the dynamic nature of numerosity selective neural populations, where neural numerosity selectivity was altered systematically in all numerosity selective brain areas. Based on findings showing brain regions which process more than one type of quantity, such as numerosity and time, we proceeded to use cross-adaptation to numerosity and time to study whether neural populations selective for numerosity or time interact. We found an unbalanced interaction between numerosity and time where adaptation to time affected numerosity perception but not the other way around. After finding this interaction between neurons selective for processing numerosity and time, further experiments showed that the neural populations underlying the effect of adaptation to time on numerosity perception are partially distinct from those underlying the effect of the time of adaptation on numerosity perception. Collectively, these results highlight that there are partially overlapping neural mechanisms which are dedicated for processing both numerosity and time. We propose that neurons which are selective or are ‘tuned’ to different quantities such as number, time or size are fundamental to understanding quantity perception. We illustrate how the properties of quantity-tuned neurons can underlie various perceptual phenomena. We further show that quantity-tuned neurons are organized in distinct but overlapping neural networks. We suggest that this overlap in tuning provides the neural basis for perceptual interactions between different quantities

Adaptation reveals unbalanced interaction between numerosity and time

Processing quantities such as the number of objects in a set, size, spatial arrangement and time is an essential means of structuring the external world and preparing for action. The theory of magnitude suggests that number and time, among other continuous magnitudes, are linked by a common cortical metric, and their specialization develops from a single magnitude system. In order to investigate potentially shared neural mechanisms underlying numerosity and time processing, we used visual adaptation, a method which can reveal the existence of a dedicated processing system. We reasoned that cross-adaptation between numerosity and duration would concur with the existence of a common processing mechanism, whereas the absence of cross-adaptation would provide evidence against it. We conducted four experiments using a rapid adaptation protocol where participants adapted to either visual numerosity or visual duration and subsequently performed a numerosity or duration discrimination task. We found that adapting to a low numerosity altered the estimation of the reference numerosity by an average of 5 dots, compared to adapting to a high numerosity. Similarly, adapting to a short duration altered the estimation of the reference duration by an average of 43 msec, compared to adapting to a long duration. In the cross-dimensional adaptation conditions, duration adaptation altered numerosity estimation by an average of 1 dot, whereas there was not sufficient evidence to either support or reject the effect of numerosity adaptation on duration judgments. These results highlight that there are partially overlapping neural mechanisms which are dedicated for processing both numerosity and time

Distinct temporal mechanisms modulate numerosity perception

Our ability to process numerical and temporal information is an evolutionary skill thought to originate from a common magnitude system. In line with a common magnitude system, we have previously shown that adaptation to duration alters numerosity perception. Here, we investigate two hypotheses on how duration influences numerosity perception. A channelbased hypothesis predicts that numerosity perception is influenced by adaptation of onset/offset duration channels which also encode numerosity or wire together with numerosity channels (duration/numerosity channels). Hence, the onset/offset duration of the adapter is driving the effect regardless of the total duration of adaptation. A strength-of-adaptation hypothesis predicts that the effect of duration on numerosity perception is driven by the adaptation of numerosity channels only, with the total duration of adaptation driving the effect regardless of the onset/ offset duration of the adapter. We performed two experiments where we manipulated the onset/offset duration of the adapter, the adapter's total presentation time, and the total duration of the adaptation trial. The first experiment tested the effect of adaptation to duration on numerosity discrimination, whereas the second experiment tested the effect of adaptation to numerosity and duration on numerosity discrimination. We found that the effect of adaptation to duration on numerosity perception is primarily driven by adapting duration/numerosity channels, supporting the channelbased hypothesis. In contrast, the effect of adaptation to numerosity on numerosity perception appears to be driven by the total duration of the adaptation trial, supporting the strength-of-adaptation hypothesis. Thus, we show that adaptation of at least two temporal mechanisms influences numerosity perception

Distinct temporal mechanisms modulate numerosity perception

Our ability to process numerical and temporal information is an evolutionary skill thought to originate from a common magnitude system. In line with a common magnitude system, we have previously shown that adaptation to duration alters numerosity perception. Here, we investigate two hypotheses on how duration influences numerosity perception. A channelbased hypothesis predicts that numerosity perception is influenced by adaptation of onset/offset duration channels which also encode numerosity or wire together with numerosity channels (duration/numerosity channels). Hence, the onset/offset duration of the adapter is driving the effect regardless of the total duration of adaptation. A strength-of-adaptation hypothesis predicts that the effect of duration on numerosity perception is driven by the adaptation of numerosity channels only, with the total duration of adaptation driving the effect regardless of the onset/ offset duration of the adapter. We performed two experiments where we manipulated the onset/offset duration of the adapter, the adapter's total presentation time, and the total duration of the adaptation trial. The first experiment tested the effect of adaptation to duration on numerosity discrimination, whereas the second experiment tested the effect of adaptation to numerosity and duration on numerosity discrimination. We found that the effect of adaptation to duration on numerosity perception is primarily driven by adapting duration/numerosity channels, supporting the channelbased hypothesis. In contrast, the effect of adaptation to numerosity on numerosity perception appears to be driven by the total duration of the adaptation trial, supporting the strength-of-adaptation hypothesis. Thus, we show that adaptation of at least two temporal mechanisms influences numerosity perception

Transient Prepubertal Mifepristone Treatment Normalizes Deficits in Contextual Memory and Neuronal Activity of Adult Male Rats Exposed to Maternal Deprivation

Contains fulltext : 181411.pdf (publisher's version ) (Open Access)Early life adversity is a well-known risk factor for behavioral dysfunction later in life, including the formation of contextual memory; it is also (transiently) accompanied by hyperactivity of the stress system. We tested whether mifepristone (MIF) treatment, which among other things blocks glucocorticoid receptors (GRs), during the prepubertal period [postnatal days (PND)26-PND28] normalizes memory deficits in adult male rats exposed to 24-h maternal deprivation (MD) at PND3. MD reduced body weight gain and increased basal corticosterone (CORT) levels during the PND26, but not in adulthood. In adulthood, contextual memory formation of MD compared to noMD (i.e., control) male rats was significantly impaired. This impairment was fully prevented by MIF treatment at PND26-PND28, whereas MIF by itself did not affect behavior. A second behavioral test, a rodent version of the Iowa Gambling Task (rIGT), revealed that flexible spatial learning rather than reward-based aspects of performance was impaired by MD; the deficit was prevented by MIF. Neuronal activity as tested by c-Fos staining in the latter task revealed changes in the right hippocampal-dorsomedial striatal pathway, but not in prefrontal areas involved in reward learning. Follow-up electrophysiological recordings measuring spontaneous glutamate transmission showed reduced frequency of miniature postsynaptic excitatory currents in adult CA1 dorsal hippocampal and enhanced frequency in dorsomedial striatal neurons from MD versus noMD rats, which was not seen in MIF-treated rats. We conclude that transient prepubertal MIF treatment normalizes hippocampus-striatal-dependent contextual memory/spatial learning deficits in male rats exposed to early life adversity, possibly by normalizing glutamatergic transmission.1 september 201

The role of neural tuning in quantity perception

Perception of quantities, such as numerosity, timing, and size, is essential for behavior and cognition. Accumulating evidence demonstrates neurons processing quantities are tuned, that is, have a preferred quantity amount, not only for numerosity, but also other quantity dimensions and sensory modalities. We argue that quantity-tuned neurons are fundamental to understanding quantity perception. We illustrate how the properties of quantity-tuned neurons can underlie a range of perceptual phenomena. Furthermore, quantity-tuned neurons are organized in distinct but overlapping topographic maps. We suggest that this overlap in tuning provides the neural basis for perceptual interactions between different quantities, without the need for a common neural representational code