Time and Science

The following sections are included:

• Time and Science: Foreword
• Introduction to Volume 2
• Contents

The literature covering evolution has had a century and a half to assemble a vast, detailed, and nuanced understanding. Less is known regarding the role that epigenetics might play. Epigenetics encompasses the mechanisms that regulate when and where genes are activated or silenced, as opposed to the DNA sequences that encode their products. Modularization of genetic and embryological processes occurs at multiple scales and levels and is the product of both operational and temporal constraints. As the mechanism that mediates genome–environment interaction, epigenetics operates over several different and hierarchically linked temporal levels. This chapter will discuss the different operational levels of modularization, and the implications modularization has for evolutionary innovation and inertia. As the mediator, and in some instances the recorder of temporal (experiential) life, epigenetics has the potential to expand variation, provide tools that buffer environmental challenges, consolidate the directionality of change, and possibly increase evolvability…

The following sections are included:

• Introduction
• Zygotic Genome Activation
• The Segmentation Clock
• The Hox Clock
• The Circadian Clock
• Conclusion
• References

In this chapter we will question the feeling of time continuity, and its impairment in patients with schizophrenia. It may feel strange to question the continuity of time, even at the perception level, but several recent results strongly suggest that our perception is rhythmic rather than continuous. We will summarize this research and question how a feeling of time continuity can nonetheless be reached. We will argue that our feeling of time continuity is rooted in the temporal accuracy of our interaction with our environment, and will detail how millisecond-level mechanisms usually involved in automatic adjustment processes may participate in our feeling of being in continuous and accurate interaction with our surroundings. We will show that these mechanisms sometimes impact our conscious experience, and can distort it in patients with schizophrenia. The abnormal sensitivity of these patients to short asynchronies leads us to suggest that our feeling of time continuity may require us to ignore short perceptual delays.

The experience of time accompanies all aspects of humanity. Scientifically, time has been investigated across many contexts, including during normal wakeful state as well as when one is physiologically aroused, excited, psychologically anxious, depressed, bored, or fearful. Time has also been examined when an individual is cognitively engaged, loaded, attentive, or in different physical environments, from sea level to the mountain tops, from crowded cities to open fields, and from an environment of socialization to that of isolation, in the real world as well in a virtual one, from dangerous encounters to near-death experiences. In all these contexts, external sensory information enters and contributes to the subjective experience of time…

You and I, being feeling and thinking matter, age as time elapses and thus we conceive time as an irreversible arrow. We also speak of time that passes and that lasts, of time that marks the beat, and reminisce the past and plan the future times. Humans equip themselves with a linear arrow of time (sometimes circular) on which they chronologically arrange events, facts of their personal life, or those of history; events, which they causally (re)arrange from the past to anticipate the future. The intelligible and consciously available temporal phenomenology we humans experience is a hallmark of exquisite evolutionary processes, seemingly remote from the time that physics describes. Yet, the psychological reality that makes up our intangible awareness of what we call “time” is inseparable from the functioning of the most complex physical systems known in the universe: our brains. Can we infer from the dynamic properties of brain activity our experience of time? Is the timing of consciousness emerging from our brain also the consciousness of time we claim to have? Herein, I will discuss the viewpoint that (psychological) time results from a neural code and that time perception cannot be reduced to “serial nows” — if only from the external observer’s viewpoint. Operationalizing “time” in cognitive neuroscience is a necessary heuristic to posit clear computational goals, algorithmic rules, and possible implementations of mental clocks in thinking matter…

Time is at the core of the concept of memory, since memory is a skill that allows us to maintain over short to long timespans the possibility of retrieving in the present information perceived in the past and past experiences. Dated memories ground our sense of identity, temporal continuity, and self-awareness. This chapter presents specific types of memory concerned with objective and subjective time dimensions, namely episodic memory and autobiographical memory. We develop some issues on the role of time retention in the nature of memories and the concept of mental time travel as the ability to mentally project oneself backward in time to relive personal past experiences and forward in time to pre-live possible episodic future experiences. But beyond the role of episodic memory in projection in time, the objective is to highlight the findings that point out the underestimated role of personal semantics in the process of building future events.

The computational role of discharge rates of neurons in information processing in the brain seems unlikely today, even if the principle of psycho-neural identity has led to remarkable practical results. Detection of coincidences, oscillation of neuronal territories, phase setting and/or phase advances of neuronal emissions, and frequent changes in synapse efficiencies by the temporal mechanism of “spike-timing-dependent plasticity” (STDP) suggest the use by the brain of a precise temporal coding, typically up to a fraction of millisecond (ms), despite the fact that a single spike has a width of 2–3 ms. To understand the functioning of neural networks, the recording of neural discharges in animal models has been and continues to be very useful, but new non-invasive techniques nowadays allow us to ascertain the use of the same principles in the human brain.

The following sections are included:

• Introduction
• Power Efficiency
• Firing Rate-based Codes
• The Alternative: Temporal Coding
• Learning in Neural Networks
• Spike-Time-Dependent Plasticity (STDP)
• JAST: Learning with Binary Synapses
• Grandmother Cells and Neocortical Dark Matter
• Towards Terabrain Computing
• Final Comments: Adding Dynamics to Neural Processing
• References

Enquiries concerning the underlying mechanisms and emergent properties of a biological brain have a long history of theoretical postulates and experimental findings. Today, the scientific community tends to converge on a single interpretation of the brain’s cognitive underpinnings — that it is a Bayesian inference machine. This contemporary view has naturally been a strong driving force in recent developments in computational and cognitive neurosciences. Of particular interest is the brain’s ability to process the passage of time — one of the fundamental dimensions of our experience. How can we explain empirical data on human time perception using the Bayesian brain hypothesis? Can we replicate human estimation biases using Bayesian models? What insights can agent-based machine learning models provide for the study of this subject? In this chapter, we review some of the recent advancements in the field of time perception and discuss the role of Bayesian processing in the construction of temporal models.

The following sections are included:

• Different Views on the Nature of Time
• The Sources of the Discrepancies: Time Reversal Invariance of the Fundamental Physical Laws and Relativity
• Two Extreme Positions: Global Presentism and Static Eternalism
• The Key to a Solution: Time is a Multilayered Concept
• Partitioning the Land
• Differences
• References