Debapratim Jana: Investigating the Role of Layer 6b in Thalamo-Cortical Loop Activity in the Cortex

BCCN Berlin / Technische Universität Berlin

Abstract

The higher-order cortico-thalamo-cortical (CTC) loops play fundamental roles in cognition and states of consciousness, with recent findings highlighting the putative critical role of Layer 6b (L6b) in maintaining activity within these circuits. This master's thesis develops a computational spiking neural network model to investigate the mechanisms by which L6b controls higher-order thalamocortical dynamics. The model incorporates biophysically realistic components including leaky integrate-and-fire neurons with spike-frequency adaptation, T-type calcium channels in higher-order thalamic (HoT) neurons enabling rebound burst firing, and Tsodyks-Markram short-term synaptic plasticity with depression in the CTC loop and facilitation in L6b projections.

Three computational experiments test predictions of the Layer 6b Attention Theory. First, the model reproduces experimental observations of L6b photostimulation, demonstrating characteristic ramp-up dynamics and persistent activation of the CTC loop during stimulation followed by rebound oscillations mediated by T-type calcium channel de-inactivation—validating one of the model's core predictions against empirical data.

Second, a hypothetical subliminal perception paradigm examines how L6b support determines the persistence of CTC activity that may be central to sustained awareness and perception: without L6b input, sensory-evoked activity decays within approximately 100 ms due to synaptic depression; with transient L6b activation, activity persists moderately longer; while sustained L6b input enables CTC activity to exceed the ~200 ms threshold associated with conscious access. This demonstrates computationally how L6b may gate the transition from subliminal to conscious perception.

Third, an ADHD-like attention deficit model tests the hypothesis that reduced L6b drive, resulting from lowered dopamine sensitivity in ADHD, shifts HoT neurons toward burst firing mode, increasing susceptibility to distraction. Under conditions of L6b hypofunction, the model predicts elevated T-channel burst responses to transient distractor stimuli and impaired maintenance of sustained attention—patterns consistent with thalamocortical dysrhythmia observed in ADHD and predictions of the Layer 6b Attention Theory.

Together, these simulations demonstrate how the deepest and thinnest cortical layer exerts surprisingly powerful control over brain-wide neural dynamics, potentially gating access to consciousness itself. The model generates specific, testable predictions linking L6b activity to conscious perception and attention disorders, advancing our mechanistic understanding of thalamocortical contributions to cognition.

 

 

Guests are welcome!

 

Additional information:

Master thesis defense

 

Organized by:

Prof. Matthew Larkum & Dr. Tilo Schwalger