José Vergara

A Neural Parametric Code for Storing Information of More than One Sensory Modality in Working Memory

Working memory, a well-studied cognitive function, refers to the capacity to remember things for a short time. Which neurons in the brain implement this function and how exactly they do it are unresolved questions. Here we show that, in a cortical area that participates in the analysis of perceptual experiences, the same neurons encode both tactile and acoustic information in working memory, and do so using the same representation for both modalities. This means that memory circuits in this area are dedicated to encoding information in a relatively abstract format that had not been revealed until now.

Quantization of the Myers-Pospelov model: The photon sector interacting with standard fermions as a perturbation of QED

We study the quantization of the electromagnetic sector of the Myers-Pospelov model coupled to standard fermions. Our main objective, based upon experimental and observational evidence, is to construct an effective theory which is a genuine perturbation of QED, such that setting the Lorentz invariance violation parameters to zero will reproduce it. To this end we provide a physically motivated prescription, based on the effective character of the model, regarding the way in which the model should be constructed and how the QED limit should be approached. This amounts to the introduction of an additional coarse-graining physical energy scale M, under which we can trust the effective field theory formulation. The prescription is successfully tested in the calculation of the Lorentz invariance violating contributions arising from the electron self-energy. Such radiative corrections turn out to be properly scaled by very small factors for any reasonable values of the parameters and no fine-tuning problems are found. Microcausality violations are highly suppressed and occur only in a spacelike region extremely close to the light cone. The stability of the model is guaranteed by restricting to concordant frames satisfying 1-|v{sub max}|>6.5x10{sup -11}.

The photon sector in the quantum Myers―Pospelov model: An improved description

Abstract The quantization of the electromagnetic sector of the Myers–Pospelov model coupled to standard fermions is studied. Our main objective is to construct an effective quantum theory that results in a genuine perturbation of QED, such that setting zero the Lorentz invariance violation (LIV) parameters will reproduce it. This is achieved by introducing an additional low energy scale M , together with a physically motivated prescription to take the QED limit. The prescription is successfully tested in the calculation of the electron self-energy in the one loop approximation. The LIV radiative corrections turn out to be properly scaled by very small factors for any reasonable values of the parameters, no fine-tuning problems are found at this stage and the choice for M to be of the order of the electroweak symmetry breaking scale is consistent with the stringent bounds for the LIV parameters, in particular with those arising from induced dimension three operators.

Noncommutative spaces, the quantum of time, and Lorentz symmetry

We introduce three space-times that are discrete in time and compatible with the Lorentz symmetry. We show that these spaces are not commutative, with commutation relations similar to the relations of the Snyder and Yang spaces. Furthermore, using a reparametrized relativistic particle we obtain a realization of the Snyder type spaces and we construct an action for them.

Emergence of an abstract categorical code enabling the discrimination of temporally structured tactile stimuli

Significance What are the neural codes that allow the discrimination of two vibrotactile stimulus patterns of equal mean frequency? We recorded single-neuron activity in primary somatosensory (S1) and dorsal premotor (DPC) cortex while trained monkeys performed a challenging pattern discrimination task. We found a faithful representation of the stimuli in S1 and a heavily transformed, more abstract, and highly varied set of responses in DPC. Most notably, in addition to memory-related activity and responses encoding the monkeys’ choices, the DPC data included a large set of categorical neurons that code specific combinations of past and present stimuli and, at the same time, are strongly predictive of the monkeys’ behavior. The problem of neural coding in perceptual decision making revolves around two fundamental questions: (i) How are the neural representations of sensory stimuli related to perception, and (ii) what attributes of these neural responses are relevant for downstream networks, and how do they influence decision making? We studied these two questions by recording neurons in primary somatosensory (S1) and dorsal premotor (DPC) cortex while trained monkeys reported whether the temporal pattern structure of two sequential vibrotactile stimuli (of equal mean frequency) was the same or different. We found that S1 neurons coded the temporal patterns in a literal way and only during the stimulation periods and did not reflect the monkeys’ decisions. In contrast, DPC neurons coded the stimulus patterns as broader categories and signaled them during the working memory, comparison, and decision periods. These results show that the initial sensory representation is transformed into an intermediate, more abstract categorical code that combines past and present information to ultimately generate a perceptually informed choice.

LETTER: Gauge Invariance of Complex General Relativity

AbstractIn this paper it is implemented how to make compatible the boundary conditions and the gauge fixing conditions for complex general relativity written in terms of Ashtekar variables using the approach of Ref. [1]. Moreover, it is found that at first order in the gauge parameters, the Hamiltonian action is (on shell) fully gauge-invariant under the gauge symmetry generated by the first class constraints in the case when spacetime

Real sector of self-dual Gravity with only first class constraints

\mathcal{M}

Internal bias controls dopamine perceptual decision-related responses

has the topology % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWefv3ySLgznf% gDOfdaryqr1ngBPrginfgDObYtUvgaiuaacqWFZestcqWFaCFpcqGH% 9aqpcaWGsbGaey41aq7exLMBbXgBd9gzLbvyNv2CaeXbbjxAHXgiv5% wAJ9gzLbsttbacgaGaa43Odaaa!52EB!\[\mathcal{M} = R \times \Sigma \] = R × Σ and Σ has no boundary. Thus, the statement that the constraints linear in the momenta do not contribute to the boundary terms is right, but only in the case when Σ has no boundary.